A fire-resistant base material containing biomass fibers, an integrated fire door core, and a method for manufacturing the same

Abstract

This invention discloses a fire-retardant substrate containing biomass fibers, an integrated fireproof door core, and its preparation method, belonging to the field of fireproof doors. The fireproof substrate of this invention introduces cellulose fibers into the adhesive layer of an inorganic filler matrix system of magnesium sulfate, magnesium hydroxide, and calcium hydroxide, and incorporates a specific styrene-acrylate copolymer. Simultaneously, the length of the cellulose fibers and the two key inorganic fillers, magnesium sulfate and magnesium hydroxide, are controlled, allowing the three to form a synergistic compatibility and cross-linking effect in the adhesive layer. This effectively optimizes the distribution of the overall components in the adhesive layer. While ensuring the interlayer bonding and flame-retardant performance of the resulting product, the waterproof effect of the adhesive layer is significantly improved without the need for waterproofing or water-absorbing agents. The fireproof substrate has good interlayer connectivity, high regularity, and strong durability. The product does not experience significant performance degradation even after long-term storage or in humid environments.

Description

Technical Field

[0001] This invention relates to the field of fire doors, specifically to a flame-retardant fireproof substrate containing biomass fibers, an integrated fireproof door core, and a method for preparing the same. Background Technology

[0002] Lightweight fire-resistant substrates are common products in the field of fire doors for homes. They are mainly made of lightweight wood or composite material substrates, which are bonded and pressed together with flame-retardant adhesive coatings. They have various advantages such as being lightweight, easy to process, environmentally friendly, and flame-retardant.

[0003] However, the adhesive coatings used in existing lightweight fire-resistant substrates, apart from flame-retardant additives, mainly consist of inorganic mineral fillers and organic adhesives. For example, the door core substrate described in CN113754367A uses a cement system directly as its base component, while CN105837247A, in addition to foamed cement as a filler, also introduces organic modifiers to improve the material's bonding and dispersion effects. This type of coating has a certain tendency to absorb water after being bonded to the substrate. This can lead to interlayer separation due to internal moisture after prolonged storage or use in a humid environment. In addition to affecting interlayer bonding, the material may deteriorate due to moisture, especially the flame-retardant components, resulting in a decline in low smoke production and high smoke production when heated. Furthermore, introducing a certain amount of waterproofing agents or water-absorbing agents into the coating may reduce its bonding, making it difficult to meet the requirements of the current national research project on key bio-based substrate flame-retardant and fire-resistant enhancement technologies. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention aims to provide a fire-resistant substrate. This is achieved by introducing cellulose fibers into the adhesive layer of a magnesium sulfate, magnesium hydroxide, and calcium hydroxide inorganic filler matrix system, along with a specific styrene-acrylate copolymer. Simultaneously, the length of the cellulose fibers and the dimensions of the two key inorganic fillers, magnesium sulfate and magnesium hydroxide, are controlled to create a synergistic compatibility and cross-linking effect within the adhesive layer. This effectively optimizes the overall component distribution within the adhesive layer. While ensuring the interlayer bonding and flame-retardant properties of the resulting product, the waterproofing effect of the adhesive layer is significantly improved without the need for waterproofing or water-absorbing agents. The fire-resistant substrate exhibits good interlayer connectivity, high regularity, and durability, and its performance does not significantly degrade even after prolonged storage or in humid environments.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A fire-resistant substrate includes a plurality of substrates and an adhesive layer disposed on at least one surface of the substrates, the adhesive layer comprising the following components in parts by weight: Magnesium sulfate 45-65 parts, magnesium hydroxide 40-50 parts, calcium hydroxide 0.5-1.5 parts, styrene-acrylate copolymer 0.5-1.5 parts, cellulose fiber 1-15 parts; The average particle size of the magnesium sulfate is 0.5~1.5 mm; The average particle size of the magnesium hydroxide is ≥20μm; The average length of the cellulose fibers is 3-15 mm.

[0006] Existing lightweight fire-resistant substrates mainly use inorganic fillers (such as silicate fillers) combined with organic binders as the main components of the adhesive layer. This adhesive layer serves as an interlayer to connect and bond several substrates (mostly lightweight wood panels or composite boards). While this adhesive layer system has advantages such as lightweight, good mechanical properties, and certain flame-retardant characteristics, it also exhibits a high tendency to absorb moisture. This is especially true after the fire-resistant substrate has been processed and stored for a long time, or after use in humid environments for a period of time, leading to moisture accumulation in the adhesive layer, particularly when the substrate itself also has some hygroscopic properties. In the case of wood or composite boards, the adhesion between the substrate and the adhesive layer will decrease significantly, and in severe cases, there may be local separation. The interlayer bonding performance of the product will decrease. At the same time, affected by moisture, some components of the adhesive layer may also deteriorate or have compatibility issues, which will also reduce the product's smoke production when heated and reduce its durability. Although some improved products have introduced certain waterproof / water-absorbing agents, this may reduce the initial tack of the adhesive layer or lead to insufficient compatibility between components and low density, resulting in poor interlayer bonding of the product.

[0007] Therefore, in the technical solution of this invention, in order to balance the basic performance and waterproof durability of the product, magnesium sulfate, magnesium hydroxide, and calcium hydroxide are used as the main inorganic filler components in the adhesive layer. Based on the filling, reinforcing, and flame-retardant composite effect of the three, sufficient basic mechanical strength and flame-retardant properties are provided for the product, resulting in low smoke production. At the same time, cellulose fiber, a fiber material with high flexibility, is introduced as a compound material. After further combining it with a specific styrene-acrylate copolymer, the polar groups contained in the styrene-acrylate copolymer will form hydrogen bonds / chemical bonds with the inorganic filler and chemically crosslink with the hydroxyl groups on the surface of the cellulose fiber, thereby achieving strong connection between the components. At the same time, the styrene-acrylate copolymer can also act as an effective waterproof membrane layer in the adhesive layer, effectively isolating moisture both inside the adhesive layer and on the surface of the hydrophilic wood substrate. On the other hand, compared with other types of functional fibers (e.g., cellulose fiber), Plant fibers and polymer fibers can achieve a balance between high compatibility and high flexibility, as well as high dimensional and chemical stability (no significant expansion / shrinkage or oxidative deterioration occurs during heating or component mixing). When the adhesive layer is prepared and coated onto the substrate for curing, cellulose fibers and inorganic particles form a tight three-dimensional structure without precipitation or agglomeration. Furthermore, based on their flexible characteristics, they can apply elastic constraints to inorganic fillers and styrene-acrylate copolymers during processing and curing, significantly reducing internal gaps or cracks caused by volume changes. This results in high component density and good packing uniformity, further effectively blocking moisture intrusion. However, if other fibers are used as substitutes, fiber incompatibility may occur, or there may be many gaps inside the adhesive layer after formation, making it difficult to achieve the desired improvement in waterproofness. In fact, the presence of too many free hydrophilic groups on the fiber surface may even increase the product's water absorption tendency.

[0008] Meanwhile, in the system, the inorganic filler and cellulose fiber, which are the main structural components, need to be coordinated in size. On the one hand, the compounding ratio of the organic linking component styrene-acrylate copolymer described in this application needs to be controlled within a low ratio range. If too much is introduced, it will lead to an increase in the brittleness of the entire adhesive layer and a decrease in adhesive strength. Under the formulation ratio with a relatively low proportion of organic linker components, if the inorganic filler particles magnesium sulfate and magnesium hydroxide, especially the relatively small flame retardant magnesium hydroxide, have too small a particle size and too large a surface area, there will be too many polar groups on their surface during processing and use, which are difficult to be captured and fixed by the styrene-acrylate copolymer. These polar groups have strong hydrophilicity, which will accelerate the water absorption effect of the product and affect the durability of the product. On the other hand, if the cellulose fiber matched with the inorganic filler is too short, it may intertwine to form clumps, resulting in poor component uniformity, which in turn affects the interlayer bonding performance and even the fire resistance performance.

[0009] On the other hand, compared to magnesium hydroxide, the particle size variation of large-sized magnesium sulfate has a greater impact on the material's bulk density. If the magnesium sulfate particle size is too large, although the specific surface area decreases, reducing the number of water contact sites, the packing density between particles decreases, which in turn reduces the interlayer bonding strength of the product. Water storage spaces are easily formed between particles, and internal gaps are more likely to form during the curing stage of the adhesive layer, so the waterproof performance of the product is still not guaranteed. In addition, the length of cellulose fibers cannot be too large, otherwise this component will be mostly distributed in a two-dimensional form in the adhesive layer, which cannot fully cover and connect the inorganic filler and styrene-acrylate copolymer, affecting the interlayer bonding. This distribution is also more likely to accumulate moisture (the plane composed of discrete fibers has a large and concentrated contact area), causing local adhesive layers to easily detach due to water absorption, affecting product performance. In addition, some cellulose fibers may migrate to the outside of the adhesive layer.

[0010] It should be noted that the cellulose fiber includes single fibers with a diameter in the micrometer range, and the single fiber includes cellulose.

[0011] The cellulose fibers described in this invention include single fibers with a diameter of micrometers. These cellulose-containing single fibers can be in a free state, or they can be interwoven or superimposed. There is no specific limitation on this. Depending on the processing steps, the cellulose fibers can be discrete in a macroscopic state, or they can be sheet-like or block-like forms formed after cutting, pressing, and other processes.

[0012] It should be noted that the cellulose fiber described in this invention has a cellulose purity of ≥80wt%.

[0013] The cellulose purity of the cellulose fiber described in this invention is determined with reference to the test method in "Determination of Cellulose Content by Nitric Acid Ethanol Method" - Chemical Research 2011.

[0014] The cellulose fiber described in this invention refers to substances with a cellulose purity of 80 wt% or higher. Unlike traditional cellulose-containing fiber products, the product described in this invention requires a combination of cellulose fiber, inorganic fillers, and styrene-acrylate copolymers to ensure sufficient affinity and flexibility, thereby achieving elastic restraint and effective bonding with various components. Using fiber products with insufficient purity (such as pure plant fibers or plant fibers with low cellulose content that have only undergone simple secondary processing) makes it difficult to achieve the desired technical effect. Furthermore, the inventors' experiments revealed that even when using other fiber materials with similar flexibility to cellulose fiber, such as polyacrylonitrile fiber, the control product prepared at the same size still cannot achieve the same technical effect. In fact, during processing, it was found that commercially available flexible fibers such as polyacrylonitrile fiber are prone to agglomeration and precipitation due to compatibility issues, resulting in products with unsatisfactory appearance and performance. Therefore, in the product described in this invention, only cellulose-based cellulose fibers with specific sizes can form a synergistic combination with rigid glass fibers.

[0015] More preferably, the purity of the cellulose fiber is 80wt%~95wt%.

[0016] The cellulose fiber inevitably contains other components not exceeding 20% ​​of the cellulose fiber mass. These other components include inorganic compounds and organic substances. The inorganic compounds can be, for example, inorganic salts, inorganic oxides, etc., while the organic substances can be, for example, lignin, which is not completely separated from the same source as cellulose during the preparation process.

[0017] Preferably, the magnesium sulfate is in the range of 45 parts, 48 ​​parts, 50 parts, 52 parts, 55 parts, 58 parts, 60 parts, 62 parts, and 65 parts by weight, or any two of these values; the magnesium hydroxide is in the range of 40 parts, 42 parts, 45 parts, 48 ​​parts, and 50 parts by weight, or any two of these values; the calcium hydroxide is in the range of 0.5 parts, 0.6 parts, 0.8 parts, 1 part, 1.2 parts, and 1.5 parts by weight, or any two of these values; the styrene-acrylate copolymer is in the range of 0.5 parts, 0.8 parts, 1 part, 1.2 parts, and 1.5 parts by weight, or any two of these values; and the cellulose fiber is in the range of 1 part, 2 parts, 3 parts, 5 parts, 6 parts, 8 parts, 10 parts, 12 parts, and 15 parts by weight, or any two of these values.

[0018] Preferably, the fire-retardant substrate satisfies: A / B = 2~21, where A is the average length of cellulose fibers and B is the average particle size of magnesium sulfate.

[0019] Preferably, the fire-resistant substrate satisfies the following range: A / B = one or any two of the following values: 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 21.

[0020] More preferably, the fire-resistant substrate satisfies: A / B = 4~12.

[0021] In the adhesive layer of the fireproof substrate described in this invention, the size ratio of the large-sized magnesium sulfate inorganic filler and cellulose fibers in the inorganic filler also has a certain impact on the performance of the product. If the particle size of magnesium sulfate is too large relative to the length of cellulose fibers, i.e., the A / B ratio is small, the cellulose fibers will be too dispersed in the inorganic filler (i.e., the cellulose fibers cannot make close contact with magnesium sulfate), and the elastic restraint will be limited. Some cellulose fibers may precipitate to the surface, reducing the effect of inhibiting the formation of internal gaps. They may also be exposed in the shallow interlayer, with high water absorption and the possibility of pyrolysis when heated, thus increasing smoke production. If the length of the cellulose fiber is too long relative to the magnesium sulfate, i.e., the A / B ratio is too large, the cellulose fiber will easily curl during processing. The close contact between the large magnesium sulfate particles and the cellulose fiber will decrease, and the dispersion uniformity of the adhesive layer components will decrease, affecting the interlayer bonding and waterproof effect. When the ratio A / B of the average length of the cellulose fiber to the average particle size of the inorganic filler is preferably within the above range, the two components are packed more tightly and uniformly. The cellulose fiber is uniformly distributed in the inorganic filler and is covered by an organic layer formed by styrene-acrylate copolymer, which is beneficial to improving the basic performance, durability and water resistance of the product.

[0022] Preferably, the cellulose fiber is a biomass-derived cellulose fiber.

[0023] It should be noted that the cellulose fiber described in this invention can be a commercially available product or a self-made product. When prepared using a self-made method, it can be prepared by, but is not limited to, the following methods: Biomass is pre-chopped, washed, and dried, then placed in an alkaline extraction solution under ultrasonic conditions for extraction reaction. After solid-liquid separation, the resulting material is treated with acid to obtain the cellulose fiber.

[0024] Preferably, the biomass includes at least one of wheat straw, rice straw, peanut shells, bagasse, corn silk, corn stalks, bamboo, and wood.

[0025] Preferably, the washing process involves sequentially treating the surface with deionized water and ethanol.

[0026] Preferably, the frequency of the ultrasound is 20~50kHz.

[0027] Preferably, the extraction reaction is carried out at a temperature of 60~100℃ for 3~8 hours.

[0028] Preferably, the alkaline extract is a mixture of sodium hydroxide and hydrogen peroxide, wherein the mass concentration of sodium hydroxide in the mixture is 1-10% and the mass concentration of hydrogen peroxide is 0.1-1%.

[0029] Preferably, the liquid-to-solid ratio of the alkaline extract to the biomass is 1 g: (20~40) mL.

[0030] Preferably, the acid treatment process involves immersing the material in an acidic solution at 60-80°C for 1-2 hours.

[0031] More preferably, the acidic solution includes at least one of acetic acid solution and oxalic acid solution, with a mass concentration of 1 to 10%.

[0032] It should be noted that the average length of the cellulose fibers described in this invention can be adjusted by controlling the reaction time during the extraction reaction. The longer the reaction time, the shorter the average length of the cellulose fibers obtained. However, this is not a limitation. Those skilled in the art can also use other variable parameters, such as the temperature of the extraction reaction or the concentration of the alkaline extract used (the higher the reaction temperature, the shorter the average length; the higher the concentration of the alkaline extract, the shorter the average length). No specific limitation is made in this regard.

[0033] Preferably, the average length of the cellulose fiber is a range of one or both of the following: 3 mm, 4 mm, 5 mm, 8 mm, 10 mm, 12 mm, and 15 mm.

[0034] Preferably, the average diameter of the cellulose fibers is 5~50 μm.

[0035] It should be noted that the average length of the cellulose fibers described in this invention can be confirmed by testing, but is not limited to, the following methods: Cellulose fibers were dispersed in ethanol and then placed under an optical microscope to observe the fiber distribution in a two-dimensional plane. Fifty fibers were identified and screened, and their lengths were measured using mapping software. The average value was calculated, which is the average length of the cellulose fiber.

[0036] More preferably, the average particle size of the magnesium sulfate is one or any two of the following: 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 0.95 mm, 1 mm, 1.1 mm, 1.2 mm, 1.25 mm, 1.3 mm, 1.4 mm, and 1.5 mm.

[0037] Furthermore, the average particle size of the magnesium sulfate is 0.7~1.4 mm.

[0038] Preferably, the average particle size of the magnesium hydroxide is 20~50μm.

[0039] More preferably, the average particle size of the magnesium hydroxide is one or any two of the following: 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, and 50 μm.

[0040] More preferably, the average particle size of the magnesium hydroxide is 20~30μm.

[0041] The inventors discovered that when the average particle size of magnesium hydroxide is preferably within the above-mentioned range, its size gradient matching with that of magnesium sulfate and cellulose fibers is higher, and the performance of the product, especially its water resistance, can be further improved.

[0042] It should be noted that the average particle size of magnesium sulfate or magnesium hydroxide described in this invention can be confirmed by, but is not limited to, the following methods: Magnesium sulfate or magnesium hydroxide is dispersed in ethanol and then placed under an optical microscope to observe the particle distribution in a two-dimensional plane. Fifty particles with complete morphology are identified and screened, and their diameters are measured using mapping software. The average value is calculated, which is the average particle size of the magnesium sulfate or magnesium hydroxide.

[0043] Preferably, the adhesive layer further contains 0.5 to 2 parts by weight of glass fiber, the average length of which is 1 to 5 mm.

[0044] After combining cellulose fibers with magnesium sulfate, magnesium hydroxide, and calcium hydroxide inorganic filler system, the adhesive layer of the present invention can further introduce an appropriate amount of glass fiber for synergistic combination. This component can improve the overall rigidity of the adhesive layer, and based on its stability, the adhesive layer has better stability during processing, higher density after molding, and a smaller two-dimensional distribution probability when combined with cellulose fibers. The product not only has improved interlayer bonding, but also better waterproof performance.

[0045] It should be noted that the average length test method for glass fibers described in this application is the same as that for cellulose fibers, and will not be repeated here.

[0046] Preferably, the ratio of the average length of the cellulose fiber to the average length of the glass fiber is 1:(0.2~0.6).

[0047] Unlike cellulose fibers, glass fibers and inorganic fillers are both rigid materials. Therefore, if their length is too long, they are prone to breakage during the processing and curing of the adhesive layer due to the interaction forces between the materials, resulting in internal pores and defects. Furthermore, changes in the ratio of their length to that of cellulose fibers also affect the product's performance: a larger ratio of the average length of cellulose fibers to glass fibers makes the glass fibers more prone to aggregation during cross-linking with cellulose fibers. This not only affects the density and uniformity of the composition but also makes the glass fibers more likely to damage the substrate when in contact with it compared to inorganic filler components, leading to water-retaining pores between the adhesive layer and the substrate. Conversely, a smaller ratio, besides being prone to rigid breakage, results in a shorter water diffusion path after contact with water compared to cellulose fibers due to their inflexibility, thus affecting the product's waterproof performance. When the ratio of the average lengths of the two fibers is preferably within the aforementioned range, the product not only has better basic interlayer bonding and fire resistance with low smoke production but also superior waterproof performance and durability.

[0048] Preferably, the ratio of the average length of the cellulose fiber to the average length of the glass fiber is a range of one or both of the following: 1:0.2, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, and 1:0.6.

[0049] Preferably, the average particle size of the calcium hydroxide is 30~80μm.

[0050] Preferably, the basis weight of a single layer of the adhesive layer is 120~300g / m². 2 The density of the fire-resistant substrate is 400~800 kg / m³. 3 .

[0051] Preferably, the substrate is a wood substrate, and the thickness of a single substrate is 0.7~3mm.

[0052] More preferably, the total thickness of the substrate is 5 to 60 mm.

[0053] The fireproof substrate of the present invention, based on the specific configuration of the adhesive layer, can take into account both the bonding performance between layers and the high flame retardant performance, with low smoke production. At the same time, while maintaining the effect of being lightweight, it has good waterproof performance and can achieve good durability even in humid environments.

[0054] Preferably, the adhesive layer further contains starch, and the mass ratio of the total mass of magnesium sulfate, magnesium hydroxide, and calcium hydroxide to the mass of starch is 1:(0.1~0.2); the substrate is a wood substrate.

[0055] When constructing adhesive layers using a variety of materials such as magnesium sulfate and cellulose fibers, in addition to styrene-acrylate copolymers, a certain amount of starch needs to be introduced as a basic binding component. After gelatinization, starch can effectively combine with each component, improving the overall stability and adhesion of the material without affecting the interaction between the inorganic fillers and fiber components.

[0056] Another object of the present invention is to provide a method for preparing the fire-retardant substrate, comprising the following steps: (1) Mix starch with magnesium sulfate and heat to gelatinize the starch, to obtain mixture A; (2) Mix magnesium hydroxide, calcium hydroxide, styrene-acrylate copolymer, cellulose fiber and dispersant and add to mixture A and stir evenly. Coat the resulting gel onto the surface of the substrate to obtain a substrate with an adhesive layer. (3) Stack several substrates with adhesive layers and press and cure them in sequence to obtain the fireproof substrate.

[0057] Preferably, when the adhesive layer contains glass fibers, the glass fibers and cellulose fibers are added together to mixture A.

[0058] The method for preparing the fire-retardant substrate described in this invention has simple operation steps, low requirements for operating equipment, and can achieve industrial-scale production.

[0059] Preferably, the total thickness of the substrate is 5 to 60 mm.

[0060] Furthermore, the total thickness of the substrate is a range of one or any two of the following: 5mm, 6mm, 8mm, 9mm, 10mm, 12mm, 12.5mm, 15mm, 16mm, 18mm, 20mm, 30mm, 40mm, and 60mm.

[0061] More preferably, the moisture content of the substrate is ≤18%.

[0062] Preferably, in step (1), water is added and stirred during starch gelatinization, and the temperature during starch gelatinization is 80~90℃ and the time is 15~30min.

[0063] Preferably, the mixture A further includes functional additives, which include at least one of colorants, pH adjusters, coagulants, lubricants, and antioxidants.

[0064] More preferably, the functional additive is present in 1 to 2 parts by weight of the components of the adhesive layer.

[0065] More preferably, the pH adjuster includes at least one of boric acid and sodium tripolyphosphate.

[0066] More preferably, the coagulant includes at least one of tartaric acid and trisodium phosphate.

[0067] More preferably, the lubricant includes at least one of erucamide and stearate.

[0068] More preferably, the antioxidant includes at least one of hindered phenolic antioxidants and phosphite antioxidants.

[0069] Preferably, in step (2), the adhesive is applied to the substrate by roller coating, and the amount of adhesive applied to a single layer of the substrate by roller coating is 200~250 g / m². 2 .

[0070] Preferably, in step (3), the pressing temperature is 20~50℃ and the pressure is 12~15 kg / cm². 2 The time is 12~48 hours.

[0071] Preferably, in step (3), the curing temperature is 20~30℃ and the time is 10~24h.

[0072] Preferably, in step (3), the temperature during the curing treatment is 20~30℃ and the time is 150~200h.

[0073] Preferably, the moisture content of the fire-resistant substrate, as tested according to GB / T 17657-2022, is 8-12%.

[0074] Preferably, the formaldehyde emission of the fire-retardant substrate, tested according to GB / T 17657-2022, is ≤0.124 mg / m³. 3 .

[0075] In addition to having ideal mechanical properties, fire resistance and water resistance, the fire-resistant substrate of the present invention also meets other technical indicators of existing products, such as moisture content and formaldehyde emission.

[0076] Another object of the present invention is to provide an integrated fireproof door core, comprising the fireproof substrate described in the present invention.

[0077] Preferably, the integrated fireproof door core is obtained by stacking or combining several fireproof substrates.

[0078] The fireproof substrate described in this invention, based on actual application scenarios, can be combined in a layered or composite manner to form a fireproof door core with controllable thickness. This fireproof door core inherits the characteristics of the fireproof substrate and can be flexibly applied and adjusted in actual door panel assembly and other scenarios, making it highly practical.

[0079] Furthermore, using cellulose fibers derived from biomaterials to construct the building materials and related products described in this invention can significantly improve the economic efficiency and low-carbon environmental value of the products. While taking into account the product effects of high fire resistance and smoke prevention as well as high comprehensive performance, the products meet the research and development requirements of the national key research and development project "Low-value long-lasting fireproof and flame-retardant technology and application demonstration of biomaterials".

[0080] The beneficial effects of this invention are as follows: A fire-retardant substrate, by introducing cellulose fibers into the adhesive layer of an inorganic filler matrix system of magnesium sulfate, magnesium hydroxide, and calcium hydroxide, and by compounding a specific styrene-acrylate copolymer, while simultaneously controlling the length of the cellulose fibers and the two key inorganic fillers, magnesium sulfate and magnesium hydroxide, allows the three to form a synergistic compatibility and cross-linking effect in the adhesive layer. This effectively optimizes the distribution of the overall components in the adhesive layer. While ensuring the interlayer bonding and flame-retardant properties of the resulting product, the waterproof effect of the adhesive layer can be significantly improved without the introduction of waterproofing or water-absorbing agents. The fire-retardant substrate has good interlayer connectivity, high regularity, and good durability. The product will not experience significant performance degradation even after long-term storage or in humid environments. Attached Figure Description

[0081] Figure 1 These are physical sample images of the fire-retardant substrate obtained in Example 1 of the present invention before (left) and after (right) a combustion test. Detailed Implementation

[0082] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and comparative examples. The purpose of this description is to provide a detailed understanding of the invention, not to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this invention are commonly used reagents and instruments.

[0083] Specifically, the materials used in each embodiment and comparative example are as follows: Magnesium sulfate 1, produced by Laizhou Yuyuan Chemical Co., Ltd., CAS 10034-99-8, purity ≥99.5%, average particle size after screening is 0.7mm.

[0084] Magnesium sulfate 2, produced by Laizhou Yuyuan Chemical Co., Ltd., CAS 10034-99-8, purity ≥99.5%, average particle size 1mm after screening.

[0085] Magnesium sulfate 3, produced by Laizhou Yuyuan Chemical Co., Ltd., CAS 10034-99-8, purity ≥99.5%, average particle size after screening is 1.4mm.

[0086] Magnesium sulfate 4, produced by Laizhou Yuyuan Chemical Co., Ltd., CAS 10034-99-8, purity ≥99.5%, average particle size 2mm after screening.

[0087] Magnesium sulfate 5, produced by Laizhou Yuyuan Chemical Co., Ltd., CAS 10034-99-8, purity ≥99.5%, average particle size after screening is 0.2mm.

[0088] Magnesium hydroxide 1, a product manufactured by Xinjiecheng, with a purity ≥95% and an average particle size of 28μm after screening.

[0089] Magnesium hydroxide 2, a product manufactured by Xinjiecheng, with a purity of ≥95% and an average particle size of 44μm after screening.

[0090] Magnesium hydroxide 3, a product manufactured by Hengyuan Chemical, with a purity ≥95% and an average particle size of 22μm after screening.

[0091] Magnesium hydroxide 4, produced by Xinjiecheng, with a purity of ≥95% and an average particle size of 15μm after screening.

[0092] Calcium hydroxide, produced by Wuhan Jiyesheng Chemical Co., Ltd., with a purity of ≥95% and an average particle size of 50μm.

[0093] Styrene-acrylate copolymer 1, produced by BASF as Acronal 7588, with 99% active ingredient.

[0094] Styrene-acrylate copolymer 2, Dow Chemical OPULYN 301, 99% active ingredient.

[0095] Organosilicon waterproofing agent, a product manufactured by Fangyu Chemical, XR-602 organosilicon modified styrene-acrylic emulsion.

[0096] Phenolic resin, a product manufactured by Shandong Duoju Chemical Co., Ltd., CAS9003-35-4.

[0097] Cellulose Fiber 1: A self-made product, prepared by: pre-chopping wheat stalks into pieces less than 5cm, washing them with deionized water, immersing them in ethanol for 30min, drying them in a 60℃ oven for 2h, then extracting them under 45kHz ultrasound at a liquid-to-solid ratio of 1g:30mL in an alkaline extraction solution composed of a mixture of sodium hydroxide (8wt%) and hydrogen peroxide (2wt%) at 80℃ for 3.5h. After solid-liquid separation, the obtained material was acidified by soaking in a 5wt% acetic acid solution at 80℃ for 1h, washed with deionized water, and dried in a 60℃ oven for 2h to obtain cellulose fiber 1, with an average length of 14.2mm, an average diameter of 39μm, and a cellulose purity of 83.6wt%.

[0098] Cellulose Fiber 2: A self-made product, prepared in the same way as Cellulose Fiber 1, except that the extraction reaction time was adjusted to 5 hours, with an average length of 6 mm, an average diameter of 36.1 μm, and a cellulose purity of 84.9 wt%.

[0099] Cellulose Fiber 3: A self-made product, prepared in the same way as Cellulose Fiber 1, except that the extraction reaction time is adjusted to 8 hours. The average length is 3.2 mm, the average diameter is 34.2 μm, and the cellulose purity is 84 wt%.

[0100] Cellulose fiber 4: A self-made product, prepared by: pre-chopping corn silk, washing it with deionized water, immersing it in ethanol for 30 minutes, drying it in a 60℃ oven for 2 hours, and then extracting it in an alkaline extraction solution composed of a mixture of sodium hydroxide (5wt%) and hydrogen peroxide (1wt%) at a liquid-to-solid ratio of 1g:20mL under 30kHz ultrasonic conditions at 80℃ for 3 hours. After solid-liquid separation, the obtained material was soaked in a 5wt% acetic acid solution at 80℃ for 1 hour, washed with deionized water, and dried in a 60℃ oven for 2 hours to obtain cellulose fiber 5, with an average length of 10.5mm, an average diameter of 20μm, and a cellulose purity of 86.1wt%.

[0101] Cellulose Fiber 5: A self-made product, prepared in the same way as Cellulose Fiber 1, except that the extraction reaction time is adjusted to 2 hours, with an average length of 21 mm, an average diameter of 41 μm, and a cellulose purity of 80 wt%.

[0102] Cellulose Fiber 6: A self-made product, prepared in the same way as Cellulose Fiber 1, except that the extraction reaction time is adjusted to 8.5h, the average length is 1.9mm, the average diameter is 32μm, and the cellulose purity is 83wt%.

[0103] Cellulose Fiber 7: Taian Haoda New Materials produces crack-resistant natural sheet cellulose fiber products. After crushing and screening, the average length is 14.5mm, the average diameter is 25μm, and the cellulose purity is 85wt%.

[0104] Plant fiber: a self-made product, prepared by: pre-chopping wheat stalks into fragments less than 5cm, washing them with deionized water, immersing them in ethanol for 30min, drying them in a 60℃ oven for 2h, then extracting them in 300mL of sodium hydroxide (10wt%) solution at 90℃ for 3h under 45kHz ultrasonic conditions at a liquid-solid ratio of 1g:30mL, separating the solid and liquid, washing with deionized water, and drying them in a 60℃ oven for 2h to obtain the plant fiber, with an average length of 24mm, an average diameter of 43μm, and a cellulose purity of 75.3wt%.

[0105] Functional additive 1: pH adjuster, boric acid.

[0106] Functional additive 2: Coagulant, tartaric acid.

[0107] Starch: Tapioca flour, produced by Qiongzhong Songtao Starch Factory of Hainan Changming Food Co., Ltd., with amylopectin accounting for 80%.

[0108] Example 1 An embodiment of the fire-retardant substrate and its preparation method according to the present invention includes the following steps: (1) Mix starch and magnesium sulfate with water, heat to 85°C and stir for 20 minutes to gelatinize the starch, add functional additives and mix to obtain mixture A; (2) Mix magnesium hydroxide, calcium hydroxide, styrene-acrylate copolymer, cellulose fiber and dispersant and add to mixture A and stir evenly. The resulting gel is coated onto the substrate surface by roller coating, with a single layer basis weight of 220 g / m². 2 A substrate with an adhesive layer is required; (3) Stack several substrates with adhesive layers and sequentially perform temperature tests at 30°C and 12 kg / cm². 2 The fire-retardant substrate is obtained by pressing under pressure for 24 hours, curing at 25°C for 24 hours, and then curing at the same temperature for 168 hours. The formaldehyde emission of this fire-retardant substrate, tested according to GB / T17657-2022, is ≤0.124 mg / m³. 3 .

[0109] The ratio of the amount of starch added in step (1) to the total mass of magnesium sulfate, magnesium hydroxide and calcium hydroxide is 0.15:1, and the ratio of the mass of water added during starch gelatinization to the mass of starch is 2:1. The substrate is a single-layer 3mm thick wooden board, consisting of 4 pieces. The bottom and top two pieces are coated on only one side, while the inner two pieces are coated on both sides. The coated surfaces are bonded together, with a total thickness of 12mm.

[0110] The specific types and weight proportions of the other components used in the adhesive layer, excluding starch, in the steps described are shown in Table 1 below.

[0111] Examples 2-13 The embodiments of the fire-retardant substrate and its preparation method described in this invention differ from Embodiment 1 only in the specific types of components used in the steps and / or the weight ratio of each component, as shown in Table 1.

[0112] Comparative Example 1 A fire-resistant substrate and its preparation method are disclosed, which differ from Example 1 only in that cellulose fibers are replaced with an equal weight of plant fibers in the aforementioned steps, as shown in Table 2.

[0113] Comparative Examples 2-11 A fire-resistant substrate and its preparation method differ from Example 1 only in that the specific types and / or weight ratios of the components used in the adhesive layer, excluding starch, are different in the steps described, as shown in Table 2.

[0114] Table 1 Table 2 Example of effect 1 To verify the effectiveness of the fire-retardant substrate described in this invention, the various embodiments and comparative examples were mechanically fixed onto a 12mm thick calcium silicate board for the following tests: (1) Interlayer bonding performance test: Refer to GB / T 18101-2024 "Flame-retardant plywood" to test the bonding strength. The number of boards tested is 10 (size 1220×2440mm). The lowest value is recorded. Among them, the bonding strength ≥0.7MPa is qualified. If at least 1 out of 10 boards is unqualified, it is recorded as unqualified. (2) Flame retardant smoke generation test: Refer to GB / T 18101-2024 "Flame-retardant plywood" for individual combustion test, record the flame retardant rating and the total smoke generation in 600s (specification 1220×2440mm).

[0115] (3) Waterproof test: Parallel samples (1220×2440mm) of each embodiment and comparative example were mechanically fixed on a 12mm thick calcium silicate board and placed in a constant temperature and humidity chamber at 35℃ and 85% relative humidity for 5 days for damp heat treatment. Then they were taken out and placed in a normal room temperature and humidity environment for 24 hours. Then the same tests as in steps (1) and (2) were performed.

[0116] The test results are shown in Tables 3-1 and 4.

[0117] Table 3-1 Table 4 As can be seen from Tables 3 and 4, because the fire-retardant substrate of this invention uses magnesium sulfate, magnesium hydroxide, and cellulose fibers of specific sizes as filler components in the adhesive layer, and simultaneously introduces a styrene-acrylate copolymer compound with both compatibility and cross-linking effects, not only can the product have ideal interlayer bonding, but the minimum adhesive strength of each product during testing also reaches above 1.2 MPa. Furthermore, the overall flame retardancy rating of the product is high, and the lateral spread of the flame in the combustion test did not reach the edge of the long wings. Figure 1 As shown, all samples reached the B1 flame retardant level, demonstrating good flame retardant performance during testing. In smoke production testing, the average total smoke generation over 600 seconds could be controlled to within 32m³. 2 Within this range, the product exhibits ideal durability. Even after damp heat treatment, its excellent waterproof performance maintains high levels of interlayer bonding and flame retardancy. The minimum bond strength of each product during testing exceeds 1 MPa, and all flame retardant ratings remain unchanged. In smoke production testing, the average total smoke generation over 600 seconds can be controlled to within 45 m³. 2 Within.

[0118] Meanwhile, a comparison of Examples 1 and 4-11 shows that the size ratio of large-sized magnesium sulfate inorganic filler and cellulose fiber in the inorganic filler also has a certain impact on the product performance. When the ratio of the average length of cellulose fiber to the average particle size of magnesium sulfate (A / B) is preferably between 4 and 12, the cellulose fiber and magnesium sulfate are in close contact, the cellulose fiber has a better elastic binding effect, the cellulose fiber can always remain inside the adhesive layer without obvious shallow precipitation, and it will not curl during processing. The adhesive layer has good dispersion uniformity, the two large-sized components have good stacking effect, the adhesive layer has high density, and the product has better adhesive strength, flame retardant performance, and waterproof performance.

[0119] In contrast, the product described in Comparative Example 1 does not use cellulose fiber. Instead, it uses plant fiber, which contains some cellulose but at a lower content and retains more biomass components. As mentioned above, cellulose fiber is irreplaceable in the product of this invention. If plastic fiber or this plant fiber is used instead, as shown in the performance demonstration of the product in Comparative Example 1, it will not only be difficult to achieve the expected waterproof effect, but may even cause a significant decrease in the low smoke production effect, resulting in the low smoke production effect failing to meet the standard (the standard requirement is not higher than 50m) after damp heat treatment. 2Meanwhile, the inventors also used commercially available polyacrylonitrile fibers to replace cellulose fibers in the preparation of a control product. The product exhibited serious appearance defects, fiber components were found in the adhesive layer, and the prepared fire-retardant substrate clearly showed interlayer surface fibers. Furthermore, the adhesive strength of the product was substandard, which will not be elaborated further here.

[0120] In Comparative Examples 2 and 3, the large-particle magnesium sulfate in the products have excessively large or small particle sizes. The former hinders the improvement of interparticle density and creates water-retaining pores, resulting in low bonding strength and poor water resistance. Performance deteriorates significantly after damp heat treatment. The latter, due to their excessively small particle size, is prone to agglomeration, similarly compromising water resistance. Bonding strength decreases significantly after damp heat treatment, and smoke generation performance fails to meet standards. Similarly, in Comparative Examples 4 and 5, the cellulose fibers paired with inorganic fillers are either too long or too short, failing to balance basic and waterproof properties. Comparing Comparative Examples 6 and 7 with the aforementioned examples shows that if the size of the large-particle magnesium sulfate and cellulose fibers is inherently too large or too small, even with a suitable A / B ratio, the desired effect is difficult to achieve. A / B adjustment requires both particles to be within a specific size range, resulting in an ideal gradient size distribution of the overall composition.

[0121] While magnesium hydroxide, which constitutes a large proportion of inorganic fillers, is relatively small in size, its size also cannot be too small. As can be seen from the comparison between Comparative Example 8 and Examples 1 and 12-13, if the particle size of this component is too small, the specific surface area will be too large, and there will be more hydrophilic sites, which will affect the waterproof performance of the product. The bonding strength of the product after humid heat treatment will decrease significantly, and the amount of flue gas generated will increase. The range needs to be controlled to ensure the overall performance of the product. Furthermore, when its average particle size is preferably 20-30 μm, the water resistance of the product is even better.

[0122] In Comparative Examples 9 and 10, the former uses a commonly available silicone waterproofing agent instead of styrene-acrylate copolymer in a common board adhesive. Although the product has good waterproofing properties, its bonding strength is low. The latter is far less effective than styrene-acrylate copolymer, exhibiting low bonding strength, high smoke production, and poor waterproofing performance. This indicates that styrene-acrylate copolymer plays a crucial role in the adhesive layer of the product of this invention. When combined with inorganic fillers and cellulose fibers, it can maintain good basic properties and waterproofing even without the introduction of a waterproofing agent. However, as shown in Comparative Example 11, if the proportion of this component in the product is too high, it will also have a negative impact of low bonding strength; therefore, its content needs to be controlled.

[0123] Furthermore, the mechanical properties of the products obtained in Examples 1-3 and the existing commercially available substrates of the same type of wood-based panel were tested: The static bending strength and modulus of elasticity (cross and parallel to the grain) were tested in accordance with GB / T 18101-2024 "Flame-retardant Plywood". Ten boards (1220×2440mm) were tested, and the lowest value was recorded. The test structure is shown in Table 3-2. Table 3-2 As can be seen, compared with existing commercially available products, the fire-retardant substrate of this invention has superior mechanical properties and can achieve a high level of durability.

[0124] Example 2 As mentioned above, the inventors discovered that in the adhesive layer of the fire-retardant substrate of the present invention, in addition to cellulose fibers, glass fibers are further introduced for combination. In order to investigate the influence of the compounding ratio and type of glass fibers on the performance of the product, the following series of products were prepared with reference to the same method as in Example 1: (1) Mix starch and magnesium sulfate with water, heat to 85°C and stir for 20 minutes to gelatinize the starch, add functional additives and mix to obtain mixture A; (2) Mix magnesium hydroxide, calcium hydroxide, styrene-acrylate copolymer, cellulose fiber, glass fiber and dispersant and add to mixture A and stir evenly. The resulting gel is coated onto the substrate surface by roller coating, with a single layer basis weight of 220 g / m². 2 A substrate with an adhesive layer is required; (3) Stack several substrates with adhesive layers and sequentially perform temperature tests at 30°C and 12 kg / cm². 2 The fireproof substrate is obtained by pressing under pressure for 24 hours, curing at 25°C for 24 hours, and then curing at the same temperature for 168 hours.

[0125] The ratio of the amount of starch added in step (1) to the total mass of magnesium sulfate, magnesium hydroxide and calcium hydroxide is 0.15:1, and the ratio of the mass of water added during starch gelatinization to the mass of starch is 2:1. The substrate is a single-layer 3mm thick wooden board, consisting of 4 pieces. The bottom and top two pieces are coated on only one side, while the inner two pieces are coated on both sides. The coated surfaces are bonded together, with a total thickness of 12mm.

[0126] The specific types and weight proportions of the components used in the adhesive layer, excluding starch, in the steps described are shown in Table 5 below.

[0127] Simultaneously, a reference standard was prepared, which did not contain cellulose fibers; the fiber material was only glass fiber.

[0128] The same effect test as Example 1 was performed on the products and control products of each experimental group, and the results are shown in Table 6.

[0129] Table 5 Table 6 As can be seen from Table 6, the basic bonding strength and low smoke production performance of the product were further improved after the introduction of glass fiber. However, since it is a rigid filler, it is also easy to generate certain outward stress after its introduction, especially when it is combined with cellulose fiber. If the average length of the two is not well matched, it may affect the waterproof performance of the product. When the average length of glass fiber matches that of cellulose fiber, and the ratio of the two is further optimized in the range of 1:(0.2~0.6), the waterproof performance of the product can be further improved in addition to the basic performance.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A fire-resistant substrate, characterized in that, It includes several substrates and an adhesive layer disposed on at least one surface of the substrates, the adhesive layer comprising the following components in parts by weight: Magnesium sulfate 45-65 parts, magnesium hydroxide 40-50 parts, calcium hydroxide 0.5-1.5 parts, styrene-acrylate copolymer 0.5-1.5 parts, cellulose fiber 1-15 parts; The average particle size of the magnesium sulfate is 0.5~1.5 mm; The average particle size of the magnesium hydroxide is ≥20μm; The average length of the cellulose fibers is 3~15 mm.

2. The fire-retardant substrate as described in claim 1, characterized in that, The fire-resistant substrate satisfies the following condition: A / B = 2~21, where A is the average length of cellulose fibers and B is the average particle size of magnesium sulfate.

3. The fire-retardant substrate as described in claim 1, characterized in that, The average particle size of the magnesium hydroxide is 20~50μm.

4. The fire-retardant substrate as described in claim 1, characterized in that, The adhesive layer also contains 0.5 to 2 parts by weight of glass fiber, the average length of which is 1 to 5 mm.

5. The fire-retardant substrate as described in claim 4, characterized in that, The ratio of the average length of the cellulose fiber to the average length of the glass fiber is 1:(0.2~0.6).

6. The fire-retardant substrate as described in claim 1, characterized in that, The single-layer basis weight of the adhesive layer is 120~300 g / m². 2 The density of the fire-resistant substrate is 400~800 kg / m³. 3 .

7. The fire-resistant substrate as described in claim 1 or 6, characterized in that, The adhesive layer also includes starch and a dispersant, and the mass ratio of the total mass of magnesium sulfate and magnesium hydroxide to the mass of starch is 1:(0.1~0.2); the substrate is a wood substrate.

8. The fire-retardant substrate as described in claim 7, characterized in that, The thickness of a single substrate is 0.7~3mm.

9. The method for preparing the fire-retardant substrate as described in claim 7, characterized in that, Includes the following steps: (1) Mix starch with magnesium sulfate and heat to gelatinize the starch, to obtain mixture A; (2) Mix magnesium hydroxide, calcium hydroxide, styrene-acrylate copolymer, cellulose fiber and dispersant and add to mixture A and stir evenly. Coat the resulting gel onto the surface of the substrate to obtain a substrate with an adhesive layer. (3) Stack several substrates with adhesive layers and perform cold pressing, mold pressing and curing treatment in sequence to obtain the fireproof substrate.

10. A fireproof door core, characterized in that, Includes the fire-resistant substrate as described in any one of claims 1 to 8.

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