A low-loss flame-retardant curtain fabric and its preparation method

Abstract

This invention relates to the field of textile technology. It discloses a method for preparing low-loss flame-retardant curtain fabric, comprising: forming a double-layer structure of a fluffy flame-retardant inner layer and a dense outer coating by flame-retardant finishing of a fabric substrate; then winding and slitting the fabric into smaller rolls using a constant-tension winding device with a tension detection and adjustment unit; the outer coating homogenizes the fabric surface friction coefficient to improve winding stability and end-face neatness, while constant-tension winding reduces wrinkles and stress concentration, ensuring the coating remains intact after curing. This invention improves flame-retardant durability by constructing a double-layer flame-retardant structure with a fluffy flame-retardant inner layer and a dense outer coating. The outer coating contains nano-silica, which homogenizes the fabric surface friction coefficient, providing favorable conditions for constant-tension winding. Constant-tension winding effectively controls tension fluctuations, eliminates start-stop waste, reduces slitting loss, and protects the coating from cracks. The final product has neat end faces, a smooth fabric surface, a soft feel, and excellent sewing performance.

Description

Technical Field

[0001] This invention relates to the field of textile technology, and in particular to a low-loss flame-retardant curtain fabric and its preparation method. Background Technology

[0002] As an important textile for interior decoration and light blocking, curtain fabric's functional finishing, especially flame-retardant finishing, is receiving increasing attention. Traditional flame-retardant treatment for curtain fabrics typically involves padding, directly applying phosphorus-nitrogen-based intumescent flame retardants to the fabric surface, followed by drying and baking to adhere the flame retardant to the fibers. This method is simple and inexpensive, but has significant drawbacks: the flame retardant, physically attached to the fiber surface in particle or film form, has weak bonding strength and is easily dissolved or detached during household or commercial washing due to water penetration and mechanical rubbing, leading to a rapid decline in flame-retardant performance. To improve flame-retardant durability, some research has attempted to coat the fabric surface with polymer coatings to seal the flame retardant, such as using polyurethane or acrylic resins as a protective layer. Conventional coatings are often thick and lack density; the presence of the coating significantly alters the fabric's feel and drape, and the uniformity and adhesion of the coating itself are difficult to guarantee. Another thorny issue in the industrial production of existing flame-retardant coated fabrics is the loss during the winding and unwinding processes. Curtain fabric is typically produced in large rolls of several thousand meters, then cut into smaller rolls according to customer orders. Traditional winding equipment lacks tension control, resulting in large tension fluctuations. This causes wrinkles and uneven ends on the fabric surface, necessitating the removal of a large amount of waste material during slitting, often resulting in a loss rate of over 2%. More seriously, tension fluctuations cause uneven stress on the cured flame-retardant coating, leading to micro-cracks or even peeling within the coating, further reducing its flame-retardant durability.

[0003] In recent years, the approach of enhancing the overall performance of materials through multi-layered composite structures has achieved success in several fields. Inspired by this, the field of functional coatings for textiles has also begun to explore designs that combine inner functional layers with outer protective layers. For flame-retardant curtain fabrics, if a fluffy flame-retardant layer can be constructed inside the fabric to provide an efficient flame retardant source, while simultaneously covering the surface with a thin, dense, transparent coating, it can not only physically isolate the washing medium and prevent the flame retardant from leaching, but also create favorable conditions for subsequent constant-tension winding by homogenizing the fabric's surface friction coefficient through the coating. How to coordinate the adhesion strength of the inner flame retardant with the density of the outer coating, how to match the coating surface characteristics with the winding tension control parameters, and how to achieve low-loss, high-quality output in industrial continuous production are all problems that need to be systematically solved. Currently, there is a lack of a curtain fabric preparation method that can both guarantee flame-retardant durability and reduce winding and unwinding losses. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention discloses a low-loss flame-retardant curtain fabric and its preparation method that can ensure flame retardant performance while improving washability, reducing winding and unwinding losses, maintaining coating integrity and fabric feel.

[0005] This invention discloses a method for preparing low-loss flame-retardant curtain fabric, which includes the following steps:

[0006] The fabric substrate is treated with flame retardant to form a double-layer flame retardant structure consisting of an inner loose flame retardant structure and an outer continuous dense flame retardant coating.

[0007] The flame-retardant treated fabric is wound up using a constant tension winding device, which includes a tension detection unit and a tension adjustment unit. The tension detection unit is used to detect the tension value of the fabric during the winding process in real time, and the tension adjustment unit automatically adjusts the winding speed or braking torque according to the detected tension value to keep the fabric tension constant during the winding process.

[0008] The large roll of fabric formed by constant tension winding is cut into multiple smaller rolls;

[0009] Among them, the outer continuous dense flame-retardant coating makes the friction coefficient of the fabric surface uniform, thereby improving the stability of constant tension winding and the neatness of the end face;

[0010] Meanwhile, constant tension winding reduces fabric wrinkles and stress concentration, ensuring that the outer continuous and dense flame-retardant coating remains intact after curing.

[0011] Furthermore, flame-retardant finishing specifically includes:

[0012] Steps for constructing the inner layer of fluffy flame retardant structure: Impregnate the fabric substrate with a working liquid containing phosphorus and nitrogen-based intumescent flame retardant, then dry it at 100℃-120℃ for 3-5 minutes, and then bake it at 150℃-170℃ for 1-3 minutes to allow the flame retardant to adhere to the fabric surface and fiber gaps, forming a fluffy, stacked inner layer flame retardant structure.

[0013] Construction steps of the outer continuous dense flame retardant coating: A coating slurry containing water-based polyurethane resin, nano silica and crosslinking agent is coated on the inner flame retardant structure, and then dried and cured to form a continuous dense flame retardant coating without pinholes.

[0014] The coating slurry comprises, by weight: 100 parts waterborne polyurethane resin, 5-15 parts nano silica, 2-5 parts crosslinking agent, 0.1-0.5 parts dispersant, and 0.1-0.3 parts defoamer.

[0015] Furthermore, the phosphorus-nitrogen intumescent flame retardant is added in the form of microcapsules. The core material of the microcapsules is a compound of ammonium polyphosphate, melamine and pentaerythritol, and the wall material is melamine resin. The average particle size of the microcapsules is 1μm-5μm.

[0016] Furthermore, the dry film thickness of the outer continuous dense flame-retardant coating is 5μm-20μm, the particle size of the nano-silica is 10nm-20nm, and the coating slurry does not contain phosphorus-based flame retardants.

[0017] Furthermore, the tension detection unit includes a floating roller and a displacement sensor. The displacement sensor is a non-contact sensor that detects the displacement of the floating roller and calculates the real-time tension value of the fabric based on the displacement-tension calibration curve.

[0018] The tension adjustment unit achieves constant tension by adjusting the rotational speed of the take-up roller or the output torque of the take-up motor.

[0019] Furthermore, the non-contact displacement sensor is either a laser displacement sensor or an ultrasonic displacement sensor.

[0020] Furthermore, the constant tension winding device is also equipped with a non-stop winding mechanism that automatically switches to an empty core when the winding reaches the set length, so as to achieve continuous winding and eliminate end face wrinkles and head and tail waste caused by stopping and starting.

[0021] Furthermore, in the step of cutting into small rolls, the length of each small roll is set to be no less than 5 meters.

[0022] This invention discloses a low-loss flame-retardant curtain fabric, prepared by any of the methods described above, comprising:

[0023] The curtain roll includes a fabric substrate, an inner fluffy flame-retardant structure distributed on the surface of the fabric substrate and in the fiber gaps, and an outer continuous dense flame-retardant coating covering at least one outer surface.

[0024] The radial misalignment between adjacent layers on the small roll end of the curtain fabric roll shall not exceed 3mm, and the number of obvious creases on the fabric surface caused by uneven rolling pressure or tension fluctuations per meter length shall not exceed 2.

[0025] After the curtain roll is washed 30 times according to the washing procedure specified in GB / T17591, the damaged length measured by the vertical burning method shall not exceed 150mm.

[0026] Furthermore, the outer continuous dense flame-retardant coating has no pinholes on its surface, and the bending length measured according to ASTM D1388 standard is no more than 1.5 compared with the uncoated fabric substrate of the same batch.

[0027] When conducting a sewing test according to GB / T21294-2014 standard, there should be no tearing or enlargement of the needle hole at the sewing point.

[0028] Furthermore, the surface arithmetic mean roughness Ra of the outer continuous dense flame-retardant coating is 0.1μm-0.5μm, and the tension adjustment unit of the constant tension winding device stores a tension-speed mapping table that matches this roughness range.

[0029] The beneficial effects of this invention are:

[0030] This invention achieves low-loss production and excellent performance of flame-retardant curtain fabrics by constructing a double-layer flame-retardant system consisting of an inner layer of fluffy flame-retardant structure and an outer layer of continuous dense flame-retardant coating, combined with a constant tension winding device. The inner layer uses microencapsulated phosphorus-nitrogen intumescent flame retardant, which forms a fluffy, stacked adhesion after impregnation, drying, and baking, providing the fabric with a highly efficient and long-lasting flame-retardant source. The outer layer uses a coating slurry composed of water-based polyurethane resin, nano-silica, and a crosslinking agent. The nano-silica is a hydrophilic surface-treated type, which forms a dense coating without pinholes after coating and curing. The outer coating not only physically seals the inner flame retardant but also, through the introduction of nano-silica, controls the arithmetic mean roughness of the coating surface to 0.1-0.5 micrometers, stabilizing the static and dynamic friction coefficients of the fabric within a narrow range, thus eliminating local friction differences caused by the original yarn texture of the fabric substrate. Based on this, the constant tension winding device detects the fabric tension in real time through floating rollers and non-contact displacement sensors, and automatically adjusts the winding speed or braking torque through the tension adjustment unit. Due to the uniform friction coefficient of the fabric surface, the tension detection accuracy and response speed are improved. The radial misalignment between adjacent layers at the end face of the small roll is no more than 3mm, and the number of obvious creases on the fabric surface caused by uneven winding pressure or tension fluctuations per meter length does not exceed 2. In contrast, the misalignment of traditional winding is usually more than 8mm and the number of creases exceeds 5.

[0031] Because the winding tension is constant, the cured outer coating avoids uneven tensile and bending stress during winding, ensuring flame retardant durability and sewing performance. The ratio of the bending length to the uncoated fabric substrate, measured according to ASTM D1388, is no greater than 1.5, maintaining the curtain fabric's soft touch and good drape. During sewing tests according to GB / T21294-2014, no tears or needle hole enlargement were observed at the stitches, demonstrating excellent processing performance. The tension adjustment unit of the constant tension winding device also has a pre-stored tension-speed mapping table matched to the coating surface roughness range. When producing different batches or curtain fabrics with different roughnesses, the system can automatically call upon the optimal winding parameters for adaptive control, further improving production efficiency and quality stability. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the overall preparation process of a low-loss flame-retardant curtain fabric according to an embodiment of this application.

[0033] Figure 2This is a flowchart of the constant tension winding closed-loop control in the embodiments of this application. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, the technical solutions in the specific embodiments of the present invention will be clearly and completely described below.

[0035] This invention discloses a method for preparing low-loss flame-retardant curtain fabric, which includes the following steps:

[0036] The fabric substrate is treated with flame retardant to form a double-layer flame retardant structure consisting of an inner loose flame retardant structure and an outer continuous dense flame retardant coating.

[0037] The flame-retardant treated fabric is wound up using a constant tension winding device, which includes a tension detection unit and a tension adjustment unit. The tension detection unit is used to detect the tension value of the fabric during the winding process in real time, and the tension adjustment unit automatically adjusts the winding speed or braking torque according to the detected tension value to keep the fabric tension constant during the winding process.

[0038] The large roll of fabric formed by constant tension winding is cut into multiple smaller rolls;

[0039] Among them, the outer continuous dense flame-retardant coating makes the friction coefficient of the fabric surface uniform, thereby improving the stability of constant tension winding and the neatness of the end face;

[0040] Meanwhile, constant tension winding reduces fabric wrinkles and stress concentration, ensuring that the outer continuous and dense flame-retardant coating remains intact after curing.

[0041] A double-layer flame-retardant structure is constructed on a fabric substrate. The inner, loose flame-retardant layer is formed by impregnating a working liquid containing microencapsulated phosphorus-nitrogen intumescent flame retardants and then drying and baking. The flame retardants adhere to the fiber surface and interstices in the form of microcapsules, forming a loose, stacked structure that provides a long-lasting flame-retardant source for the fabric. The outer, continuous, dense coating is formed by coating and curing a coating slurry composed of waterborne polyurethane resin, nano-silica, and a crosslinking agent. This coating is pinhole-free and densely continuous, which on the one hand physically seals the inner flame retardant, preventing it from leaching out during washing, and on the other hand makes the coefficient of friction on the fabric surface more uniform. The uniformity of the coefficient of friction is achieved by filling the waterborne polyurethane resin with nano-silica, forming a composite surface at the micron scale. This eliminates the local differences in the coefficient of friction caused by the unevenness of yarn thickness and weave texture in the fabric substrate, making the dynamic and static coefficients of friction of the entire fabric surface stable within a narrow range. Based on this, the tension detection unit of the constant tension winding device senses the actual tension of the fabric in real time through a floating roller and a non-contact displacement sensor, and feeds the signal back to the tension adjustment unit. The PLC controller compares the actual tension with the set tension, and then adjusts the output torque of the winding motor or the speed of the winding roller, forming a closed-loop control. Because the fabric surface friction coefficient is uniform, the accuracy and response speed of tension detection are improved, avoiding misjudgment and adjustment lag caused by sudden changes in the friction coefficient. The constant winding tension allows the fabric to be wound layer by layer on the winding roller with uniform radial pressure, eliminating localized looseness or excessive tightness caused by tension fluctuations. This effectively suppresses the formation of fabric wrinkles and prevents micro-cracks from forming after the coating has cured due to uneven stress concentration.

[0042] In terms of flame retardant performance, the inner layer's fluffy flame-retardant structure provides initial flame retardancy, while the outer layer's continuous dense coating enhances wash resistance through physical sealing. After 30 washes according to the washing procedure specified in GB / T17591, the damaged length measured by the vertical burning method is still no more than 150mm, far superior to traditional single flame-retardant finishing processes. Regarding winding stability and end-face neatness, the outer coating homogenizes the fabric's friction coefficient, resulting in a radial misalignment between adjacent layers at the end of the small roll of fabric no more than 3mm. The number of noticeable creases per meter caused by uneven winding pressure or tension fluctuations does not exceed 2, while traditional ordinary winding typically results in misalignment exceeding 8mm and more than 5 creases. In terms of slitting loss, the constant tension winding combined with a non-stop roll-changing mechanism eliminates head and tail waste caused by start-stop cycles. Simultaneously, the smooth, wrinkle-free fabric surface reduces trimming losses, reducing the slitting loss rate from over 2% in traditional processes to below 1%, thus lowering production costs and material waste. Regarding coating integrity, constant tension winding avoids the cured coating from being subjected to alternating bending and tensile stresses. Scanning electron microscopy confirmed that the coating surface is free of microcracks, thus ensuring flame retardant durability and sewing performance. Sewing tests conducted according to GB / T21294-2014 showed no tearing or needle hole enlargement at the sewing needle. The addition of nano-silica to the dense outer coating imparts a uniform coefficient of friction without significantly sacrificing fabric softness. The ratio of the bending length to the uncoated fabric substrate, measured according to ASTM D1388, is no greater than 1.5, and the arithmetic mean roughness Ra of the coating surface can be controlled between 0.1μm and 0.5μm. This facilitates the pre-storage of a tension-speed mapping table matching this roughness range in the tension adjustment unit of the constant tension winding device, enabling rapid adaptive adjustment of winding parameters for different batches of products. This method, through the synergistic cooperation of a double-layer flame-retardant structure and constant tension winding, achieves the industrial-scale production of flame-retardant curtain fabrics with low loss, high quality, and high washability.

[0043] Although the outer continuous dense flame-retardant coating forms a cross-linked network through high-temperature curing, it is not a completely rigid, stress-free state. During subsequent winding, the fabric is wound onto the core, and the coating bears the bending deformation and interlayer pressure along with the fabric. If the winding tension fluctuates too much, microcracks may appear in localized areas of the coating due to excessive tensile or compressive stress. These microcracks can compromise the coating's density, becoming channels for water and detergent penetration during washing, thus reducing flame-retardant durability. Constant tension winding, by maintaining a constant radial pressure distribution, avoids stress concentration, ensuring the coating remains intact and crack-free during winding.

[0044] As one implementation method, flame retardant finishing specifically includes:

[0045] Steps for constructing the inner layer of fluffy flame retardant structure: Impregnate the fabric substrate with a working liquid containing phosphorus and nitrogen-based intumescent flame retardant, then dry it at 100℃-120℃ for 3-5 minutes, and then bake it at 150℃-170℃ for 1-3 minutes to allow the flame retardant to adhere to the fabric surface and fiber gaps, forming a fluffy, stacked inner layer flame retardant structure.

[0046] Construction steps of the outer continuous dense flame retardant coating: A coating slurry containing water-based polyurethane resin, nano silica and crosslinking agent is coated on the inner flame retardant structure, and then dried and cured to form a continuous dense flame retardant coating without pinholes.

[0047] The coating slurry comprises, by weight: 100 parts waterborne polyurethane resin, 5-15 parts nano silica, 2-5 parts crosslinking agent, 0.1-0.5 parts dispersant, and 0.1-0.3 parts defoamer.

[0048] The inner layer of fluffy flame-retardant structure is constructed using a padding method. The fabric substrate is immersed in a working solution containing a phosphorus-nitrogen-based intumescent flame retardant, and then subjected to two dips and two pads to ensure the working solution fully penetrates the fiber surface and the gaps within the yarn. Subsequently, it is dried at 100℃-120℃ for 3-5 minutes to allow moisture to evaporate slowly and flame retardant particles to be evenly deposited on the fiber surface. Then, it is baked at 150℃-170℃ for 1-3 minutes to promote cross-linking or self-cross-linking of the active components in the flame retardant with the fiber, forming a firmly adhered, fluffy, and stacked flame-retardant layer. Drying below 100℃ will result in residual moisture and uneven migration of the flame retardant; drying above 120℃ may cause premature softening of the microcapsule wall material, damaging its structure. The baking temperature is controlled between 150℃ and 170℃ to ensure sufficient cross-linking reaction while avoiding excessively high temperatures that could lead to decreased fabric strength or decomposition of the flame retardant. The outer continuous and dense flame-retardant coating is applied using rotary screen coating or blade coating methods. A slurry composed of waterborne polyurethane resin, nano-silica, and a crosslinking agent is uniformly coated onto the surface of the fabric, which already has an inner flame-retardant structure. The waterborne polyurethane resin, as the film-forming substance, possesses excellent flexibility and adhesion to the fabric. The nano-silica, with a particle size of 10-20 nm, is uniformly dispersed in the polyurethane matrix, forming a dense physical barrier after the coating dries and cures. This effectively fills the free volume between resin molecular chains, resulting in a pinhole-free and continuously dense coating. The rigid particles of nano-silica can adjust the microstructure of the coating surface, controlling its arithmetic mean roughness between 0.1-0.5 µm. The addition of the crosslinking agent promotes the formation of a three-dimensional network structure between polyurethane molecular chains, increasing the crosslinking density and water resistance of the coating. The proportions of each component in the coating slurry have been optimized. Using 100 parts of waterborne polyurethane resin as a baseline, 5-15 parts of nano-silica ensure both density and prevent excessive brittleness. 2-5 parts of crosslinking agent achieve a suitable degree of crosslinking; the crosslinking agent can be selected from at least one of aziridine, blocked isocyanate, or carbodiimide derivatives. Dispersants and defoamers are used to ensure slurry stability and bubble-free coating. The drying and curing steps transform the coating from a liquid to a solid dry film. The dry film thickness is controlled between 5-20 µm; too thin a film results in insufficient density, while too thick a film affects flexibility.

[0049] The inner layer of loosely packed microcapsule flame retardant has a high specific surface area, which allows it to quickly form an expanded char layer during combustion, providing heat and oxygen insulation. The initial vertical burning damage length can be controlled within 80-120mm, with zero afterflame time. The outer layer of continuous, pinhole-free, dense coating forms a physical shield for the inner flame retardant, effectively resisting water molecule penetration and mechanical rubbing during household or commercial washing. This makes it difficult for phosphorus and nitrogen-based flame retardants to dissolve. After 30 washes according to GB / T17591, the damage length is still no more than 150mm, and the wash resistance is more than three times better than that of processes without an outer coating. Uncoated fabrics, due to uneven yarn thickness and variations in weaving structure, exhibit significant fluctuations in surface friction coefficient, leading to unstable tension detection during winding. In contrast, the water-based polyurethane and nano-silica composite coating creates a uniform, low-friction surface, minimizing fluctuations in the dynamic friction coefficient across the entire fabric. This provides a precise detection basis for the constant tension winding device, ensuring that the radial misalignment of the small roll end face is controlled within 3mm, and the number of pleats per meter does not exceed two. The coating slurry does not contain phosphorus-based flame retardants, avoiding interference between the outer and inner coating layers during high-temperature curing. Furthermore, the appropriate addition of nano-silica ensures the coating surface roughness falls within the optimal range of 0.1-0.5µm, facilitating the pre-storage of a matching tension speed mapping table in the tension adjustment unit for adaptive winding of fabrics with varying roughness. The bending length ratio is controlled within 1.5, guaranteeing the hand feel of the curtain fabric. Sewing tests show no tears or enlarged needle holes at the seams, demonstrating excellent processing performance.

[0050] The outer continuous dense flame-retardant coating of this invention primarily serves as a physical barrier and surface homogenization function, without providing flame-retardant functionality. The inner microencapsulated intumescent flame retardant already provides sufficient flame-retardant effect. Adding phosphorus-based flame retardants to the outer layer could lead to competitive reactions or migration with the inner layer flame retardants during high-temperature curing, and may also reduce the coating's density and abrasion resistance. Therefore, not adding phosphorus-based flame retardants to the outer coating slurry is an optimized technical choice.

[0051] As one implementation method, the phosphorus-nitrogen intumescent flame retardant is added in the form of microcapsules. The core material of the microcapsules is a compound of ammonium polyphosphate, melamine and pentaerythritol, and the wall material is melamine resin. The average particle size of the microcapsules is 1μm-5μm.

[0052] Phosphorus-nitrogen intumescent flame retardants are added in microcapsule form. The core material is a mixture of ammonium polyphosphate, melamine, and pentaerythritol in a certain proportion, and the wall material is melamine resin. The average particle size of the microcapsules is controlled between 1µm and 5µm. Microcapsules can be prepared using in-situ polymerization or interfacial polymerization. Taking in-situ polymerization as an example, the core material components—ammonium polyphosphate, melamine, and pentaerythritol—are first physically mixed at a mass ratio of, for example, 3:1:1 and ground to sub-µm size, then uniformly dispersed in an aqueous phase to form a core material emulsion. Subsequently, melamine resin prepolymer is added to the system. Under appropriate pH and temperature conditions, the melamine resin prepolymer undergoes a condensation reaction on the surface of the core material droplets, gradually depositing to form a dense melamine resin wall material. By controlling the reaction time, stirring speed, and monomer concentration, the average particle size of the microcapsules can be controlled within the range of 1µm to 5µm. When the particle size is less than 1µm, the microcapsules have an excessively large specific surface area, making them prone to aggregation, and the thin wall material leads to a decrease in encapsulation efficiency. When the particle size is greater than 5µm, the microcapsules tend to settle in the padding working solution, making it difficult to uniformly adhere to the fine fiber gaps. After microencapsulation, the microcapsules are formulated with dispersants, penetrants, and crosslinking agents to create an inner working solution. When the fabric is padded with this working solution, microcapsules with a particle size of 1µm-5µm can smoothly enter the tiny gaps inside the fiber bundles and between individual fibers. During the subsequent drying and baking processes, the melamine resin wall material softens moderately or crosslinks with the active groups on the fibers, firmly anchoring the core material to the fiber surface and interior, forming a loose, stacked flame-retardant structure. The melamine resin wall material itself contains nitrogen, which can decompose at high temperatures to produce non-flammable gases, synergistically enhancing the expansion flame-retardant mechanism of the core material.

[0053] In the core material, ammonium polyphosphate serves as the acid source, melamine as the gas source, and pentaerythritol as the carbon source, forming a classic intumescent flame-retardant system. When heated, ammonium polyphosphate decomposes to generate polyphosphoric acid, causing pentaerythritol to dehydrate and char. Simultaneously, melamine decomposes to release non-combustible gases such as ammonia, driving the char layer to expand and form a dense, porous thermal barrier, effectively preventing flame spread and heat transfer. Encapsulating all three components within the same microcapsule ensures that the acid, gas, and carbon sources are released simultaneously and react according to stoichiometric ratios during combustion, avoiding the reduced flame-retardant efficiency caused by differences in particle size and uneven dispersion of components in traditional physical mixing methods. The melamine resin wall material not only provides physical insulation, preventing the core material from absorbing moisture or reacting with external substances during storage and transportation, but more importantly, it allows for partial melt bonding with fibers, especially polyester fibers, during fabric impregnation with the working solution and subsequent drying and baking processes. This improves the adhesion between the flame retardant and the substrate, reducing mechanical loss during washing. The microcapsule size of 1µm-5µm is a reasonable match with the diameter of ordinary polyester fibers of about 10-20µm. It can be embedded in the fiber gaps rather than just piled up on the fabric surface, making the inner flame-retardant structure more fluffy and wear-resistant.

[0054] In one embodiment, the dry film thickness of the outer continuous dense flame-retardant coating is 5μm-20μm, the particle size of the nano-silica is 10nm-20nm, and the coating slurry does not contain phosphorus-based flame retardants.

[0055] The selection of nano-silica particle size is based on its compatibility with the waterborne polyurethane resin matrix. Silica particles in the 10nm-20nm range possess extremely high specific surface area and surface activity, enabling them to be uniformly dispersed among polyurethane molecular chains, forming a nanometer-scale organic-inorganic hybrid network. When the coating slurry is applied to the fabric surface via rotary screen coating or blade coating, the wet film thickness is adjusted according to the target dry film thickness and the slurry's solid content. For example, a slurry with approximately 40% solid content can achieve a wet film thickness of approximately 12µm-50µm to obtain a dry film of 5-20µm. During drying and curing, moisture and additives evaporate, and the waterborne polyurethane molecular chains undergo cross-linking reactions. The nano-silica particles act as physical cross-linking points and fillers. Because the size of the nanometer particles is much smaller than the wavelength of visible light, the coating remains transparent and does not affect the fabric's appearance. When the thickness is less than 5µm, the coating continuity is insufficient, posing a risk of pinholes or incomplete coverage, and the inner layer flame retardant may still dissolve during washing. When the thickness is greater than 20µm, the coating rigidity is too strong, and the bending length ratio easily exceeds 1.5, affecting the feel and drape of the curtain fabric, while also increasing material costs and production energy consumption. The inner layer already provides sufficient expansion flame retardancy through phosphorus-nitrogen microcapsules, and the outer layer only needs to serve as a physical barrier and surface homogenization function. If phosphorus-based flame retardants are added to the outer layer, they may compete with the inner layer flame retardant or migrate during high-temperature curing, and may also reduce the density and abrasion resistance of the coating. The outer layer slurry consists only of waterborne polyurethane, nano-silica, and a small amount of additives, without flame retardants, ensuring the purity and stability of the film.

[0056] Silica particles with a diameter of 10-20 nm fully fill the free volume between polyurethane molecular chains, reducing the oxygen and water vapor permeability of the coating and effectively preventing water and detergent from penetrating into the inner layer during washing. A dry film thickness of 5-20 µm balances protection and softness. Within this thickness range, the bending length ratio is controlled below 1.5, maintaining a soft touch and good drape for everyday use. The uniform dispersion of nano-silica creates a micro-nano composite structure on the coating surface, with an arithmetic mean roughness Ra that remains stable within the range of 0.1 µm-0.5 µm. This roughness range ensures a uniform coefficient of friction, providing stable detection conditions for constant tension winding, while avoiding slippage between winding layers caused by an overly smooth surface. The coating slurry does not contain phosphorus-based flame retardants, eliminating the risk of chemical incompatibility between the inner and outer layers. At a curing temperature of 150℃, the pure polyurethane nano silica system exhibits excellent thermal stability, with no small molecule precipitates contaminating the equipment, while avoiding the yellowing or sticky feel of fabrics that may be caused by phosphorus-based flame retardants.

[0057] In one implementation, the tension detection unit includes a floating roller and a displacement sensor. The displacement sensor is a non-contact sensor. It detects the displacement of the floating roller and calculates the real-time tension value of the fabric based on the displacement-tension calibration curve.

[0058] The tension adjustment unit achieves constant tension by adjusting the rotational speed of the take-up roller or the output torque of the take-up motor.

[0059] The tension detection unit in the constant tension winding device employs a structure of a floating roller combined with a non-contact displacement sensor. The tension adjustment unit achieves constant tension control by adjusting the winding roller speed or the braking torque of the magnetic powder brake. The fabric passes over a freely floating roller in the winding path. One or both ends of this floating roller are equipped with elastic elements such as springs or cylinders, applying a constant initial tension to the fabric. When the actual tension of the fabric changes, the balance of the net force on the floating roller is disrupted, causing the roller to shift upwards or downwards. The displacement sensor, using a non-contact method such as a laser displacement sensor or an ultrasonic displacement sensor, monitors the positional change of the floating roller in real time, outputting an electrical signal that is linearly or proportionally related to the displacement. This signal is transmitted to the PLC controller, which pre-stores the corresponding curve between displacement and tension obtained through experimental calibration—the displacement-tension calibration curve. With the device stationary, a series of known standard tension values ​​are applied to the fabric, and the corresponding floating roller displacements are recorded. A mathematical relationship or lookup table is then obtained through fitting. During normal operation, the controller calculates the actual tension of the fabric by referring to the calibration curve based on the real-time displacement value. Upon receiving the deviation signal between the actual tension and the set tension, the tension adjustment unit executes the corresponding adjustment action. If adjusting the winding roller speed, the controller changes the speed of the winding motor via a frequency converter, increasing or decreasing the winding speed, thereby changing the tension of the fabric on the floating roller and pulling the tension back to the set value. If adjusting the magnetic powder brake, the controller changes the input current to the magnetic powder brake, thereby changing its output braking torque and achieving constant tension. The non-contact displacement detection of the floating roller avoids the frictional resistance, wear, and signal drift that may occur with contact sensors, ensuring detection accuracy and long-term stability.

[0060] As one implementation method, the non-contact displacement sensor is a laser displacement sensor or an ultrasonic displacement sensor.

[0061] As one implementation method, the constant tension winding device is also equipped with a non-stop winding mechanism, which automatically switches to an empty core when the winding reaches the set length, so as to achieve continuous winding and eliminate end face wrinkles and head and tail waste caused by stopping and starting.

[0062] Furthermore, in the step of cutting into small rolls, the length of each small roll is set to be no less than 5 meters.

[0063] A non-stop roll-changing mechanism typically consists of a rotary take-up frame, a spare shaft seat, a cutting device, and pressure rollers. When the take-up length reaches a set value, such as 1500 meters, the controller issues a roll-changing command. The rotary frame rotates, bringing the empty roll core into the take-up station. Simultaneously, the pressure rollers press the fabric against the surface of the empty roll core, and the cutter automatically cuts the fabric. The fabric end is then adhered or adsorbed onto the new roll core, while the old roll core is transferred to the unloading station. The entire roll-changing process is completed automatically during continuous operation of the equipment without stopping. Meanwhile, in the step of cutting into smaller rolls, the length of each roll is set to be no less than 5 meters. This minimum 5-meter setting is optimized based on actual application scenarios: the common multiples for finished curtain widths and fixed-height cutting are integers in meters. Rolls longer than 5 meters facilitate subsequent sewing and installation and effectively reduce the frequency of roll-changing. As a preferred method, the length of the smaller rolls can be directly set to 100 meters to reduce transportation costs; after transportation to the destination, downstream manufacturers can then cut them a second time into the finished curtain length as needed.

[0064] This invention discloses a low-loss flame-retardant curtain roll, comprising:

[0065] The curtain roll includes a fabric substrate, an inner fluffy flame-retardant structure distributed on the surface of the fabric substrate and in the fiber gaps, and an outer continuous dense flame-retardant coating covering at least one outer surface.

[0066] The radial misalignment between adjacent layers on the small roll end of the curtain fabric roll shall not exceed 3mm, and the number of obvious creases on the fabric surface caused by uneven rolling pressure or tension fluctuations per meter length shall not exceed 2.

[0067] After the curtain roll is washed 30 times according to the washing procedure specified in GB / T17591, the damaged length measured by the vertical burning method shall not exceed 150mm.

[0068] In the fluffy flame-retardant structure, microcapsules with an average particle size of 1µm-5µm are embedded inside the fabric yarns and in the gaps between fibers. After drying and baking, they form a stacked adhesion, which not only provides sufficient flame retardant source for the fabric but also maintains the fabric's breathability and softness. The outer continuous dense coating uniformly covers at least one surface of the fabric with a dry film thickness of 5µm-20µm. Its nano-silica particles have a size of 10nm-20nm and crosslink with water-based polyurethane to form a pinhole-free and continuous barrier layer. Due to the presence of the outer coating, the coefficient of friction of the fabric surface tends to be uniform, so that the tension fluctuation is strictly controlled within ±5% during constant tension winding. As a result, the radial misalignment between adjacent layers on the end face of the final product's roll is no more than 3mm, and the number of obvious creases on the fabric surface caused by uneven winding pressure or tension fluctuations per meter does not exceed 2. After being washed 30 times according to the washing procedure specified in GB / T17591, the damaged length measured by the vertical burning method is no more than 150mm. This performance is mainly attributed to the anti-leaching ability of the inner microcapsule flame retardant and the physical sealing effect of the outer coating.

[0069] The radial misalignment is no more than 3mm and there are no more than 2 pleats per meter, indicating high product roll quality. The radial misalignment is measured by taking a small roll after winding and selecting three different angles on the end face. The radial offset distance between the innermost and outermost layers is measured, and the average value is taken as the radial misalignment. In subsequent garment or home textile processing, the neatly finished fabric roll can be directly fed into an automatic cutting machine without manual end-face trimming, avoiding size deviations in the cut pieces caused by misalignment. The number of pleats per meter does not exceed 2, indicating that almost no permanent creases were formed on the fabric during the winding process. For curtain fabrics with an nm coating, creases not only affect aesthetics but also disrupt the continuity of the coating, reducing the flame-retardant protection effect. The product of this invention has a smooth fabric surface, allowing for direct sewing and packaging without ironing or shaping, saving production costs and time. After 30 washes, the damaged length is still no more than 150mm, far exceeding the requirements for ordinary flame-retardant fabrics in national standards. Curtain fabrics maintain long-term flame-retardant safety during home or commercial washing. Even after multiple uses and washes, they can still effectively suppress the spread of flames in the event of a fire, protecting personal and property safety.

[0070] As one implementation method, the outer continuous dense flame-retardant coating has no pinholes on its surface, and the bending length measured according to ASTM D1388 standard is no more than 1.5 compared with the uncoated fabric substrate of the same batch.

[0071] When conducting a sewing test according to GB / T21294-2014 standard, there should be no tearing or enlargement of the needle hole at the sewing point.

[0072] The absence of pinholes on the coating surface is mainly attributed to three factors: First, the nano-silica particles, with a diameter of 10nm-20nm, are uniformly dispersed in the water-based polyurethane resin. These nano-sized particles can fill the tiny gaps between resin molecular chains, eliminating micropores caused by solvent evaporation or cross-linking shrinkage. Second, 0.1-0.3 parts of defoamer are added to the coating slurry, effectively inhibiting the formation of bubbles during coating and preventing pinholes from being left after bubble rupture. Third, the wet film thickness is controlled uniformly during rotary screen coating or blade coating, and the curing temperature is increased in a stepped manner. Drying is first carried out at a low temperature of 100℃ to allow moisture to escape slowly, followed by cross-linking at a high temperature of 150℃, preventing the defect of skin formation on the coating surface due to rapid heating, which prevents internal bubbles from escaping. A bending length ratio not exceeding 1.5 depends on the dry film thickness and the nano-silica content. When the dry film thickness is controlled between 5µm and 20µm and the nano-silica content is 5-15 parts, the increase in rigidity imparted to the fabric by the polyurethane coating is limited, and the bending length ratio is between 1.25 and 1.35. If the film is too thick or contains too much nano-silica, the coating will become too hard, with a ratio exceeding 1.5, affecting the feel and drape. In the sewing test, there were no tears or enlarged needle holes at the needle insertion point. This is due to two main factors: firstly, the coating itself possesses flexibility and elongation at break; the crosslinking degree of the waterborne polyurethane resin was optimized, ensuring both strength and elasticity; secondly, the dense, needle-free coating allows for localized elastic deformation rather than brittle cracking when the needle is inserted. After the needle is withdrawn, the coating shrinks and adheres tightly to the yarn, preventing the formation of enlarged holes or tear extension. Furthermore, the presence of a loose inner structure provides a buffer space for the fabric substrate, reducing the concentrated stress on the coating caused by the needle.

[0073] In one implementation, the surface arithmetic mean roughness Ra of the outer continuous dense flame-retardant coating is 0.1μm-0.5μm, and the tension adjustment unit of the constant tension winding device stores a tension-speed mapping table that matches this roughness range.

[0074] When the nano-silica particle size is 10nm-20nm and the addition amount is 5-15 parts, the nano-particles form a uniform micro-nano protrusion structure on the polyurethane coating surface, stabilizing Ra at 0.1-0.5µm. The surface arithmetic mean roughness Ra is measured within a 1mm × 1mm area using a white light interferometer. If the roughness is below 0.1µm, the coating is too smooth, and slippage between layers is easy during winding; if it is above 0.5µm, the coefficient of friction is too high, and the winding tension fluctuation is aggravated. The tension-speed mapping table is established as follows: for standard samples with different roughness, calibration experiments are performed on the winding device, and the speed curve that minimizes tension fluctuation is measured. The corresponding relationship is stored in the PLC controller. When changing to different batches of fabric, the operator inputs the measured Ra value or the system automatically detects it, and the controller automatically calls the matching mapping table parameters.

[0075] A surface roughness of 0.1-0.5µm provides optimal friction conditions for constant tension winding. Within this range, the friction between the fabric surface and the winding roller and guide roller is moderate, ensuring stable traction transmission while avoiding sudden tension changes caused by excessive slippage or excessive friction.

[0076] Example 1

[0077] The complete solution of this invention includes an inner layer microcapsule fluffy flame-retardant structure, an outer layer dense coating, constant tension winding, and optimized slitting.

[0078] I. Pre-processing

[0079] The polyester woven fabric was treated in a desizing and scouring solution at 80°C for 30 minutes. The desizing and scouring solution contained 3g / L NaOH and 2g / L scouring agent. The fabric was then washed with hot water, cold water, and dried.

[0080] II. Construction of the inner layer's fluffy flame-retardant structure

[0081] The inner working solution was prepared by weight as follows: 180 parts of phosphorus-nitrogen intumescent flame retardant microcapsules, 3 parts of sodium polyacrylate dispersant, 1.5 parts of JFC penetrant, 8 parts of blocked isocyanate crosslinking agent, and water to a total of 1000 parts. The core material of the microcapsules was a compound of ammonium polyphosphate, melamine, and pentaerythritol in a mass ratio of 3:1:1, and the wall material was melamine resin with an average particle size of 3 μm. The fabric was dipped into the working solution on a two-dip, two-roll mill with a roll-off rate of 75%, then dried at 110°C for 3 minutes, and then baked at 160°C for 2 minutes to obtain a fluffy flame-retardant inner layer structure.

[0082] III. Construction of the outer continuous dense coating

[0083] The coating slurry, by weight, comprises: 100 parts of waterborne polyurethane resin (polyether type, 40% solids content); 10 parts of nano-silica (15nm particle size); 3 parts of aziridine crosslinking agent; 0.3 parts of dispersant; 0.2 parts of defoamer; and deionized water to adjust the viscosity to 3500 cP. The coating slurry is applied to one side (front side) of the fabric using a rotary screen coating machine, with a wet film thickness of 35 μm. It is then dried at 100℃ for 2 minutes and cured at 150℃ for 3 minutes, resulting in a dry film thickness of approximately 12 μm.

[0084] IV. Constant tension winding

[0085] A constant tension winding device is used, comprising a floating roller, a laser displacement sensor, a PLC controller, and a magnetic powder brake. Calibration steps: Displacement-tension curves of the coated fabric under different tensions are measured and stored in the controller, and a tension-speed mapping table is established for different surface roughness Ra. The winding tension is set to 80N, corresponding to a fabric with a surface roughness Ra of approximately 0.25μm. The initial winding speed is 30m / min. The controller adjusts the magnetic powder brake current in real time based on the floating roller displacement to ensure tension fluctuations do not exceed ±3%. The device is also equipped with a non-stop winding mechanism that automatically switches to an empty core when the roll reaches 1500 meters, achieving continuous winding without downtime.

[0086] V. Division into Volumes

[0087] The 1500-meter roll was cut into smaller rolls of 10 meters each, totaling 150 rolls. Since the roll changing was done without stopping the machine, the waste at the beginning and end was eliminated. Each roll only had extremely short beginning and end due to cutting, totaling less than 0.05 meters per roll. The total loss was about 7.5 meters, with a loss rate of 0.5%.

[0088] Product Performance: Initial vertical burning test according to GB / T5455: afterflame time 0 seconds, no dripping, damage length 85mm. After 30 washes according to the washing procedure specified in GB / T17591, damage length 110mm, meeting the requirement of not exceeding 150mm. Radial misalignment at the winding end face not exceeding 2mm, and no more than one pleat per meter. Scanning electron microscopy at 1000x magnification shows the outer coating is continuous and free of pinholes, with an arithmetic mean surface roughness Ra of 0.25μm. Abrasion resistance test according to GB / T21196: no peeling after 500 cycles of friction. Bending length measured according to ASTM D1388: 45mm on uncoated substrate, 58mm after coating, ratio 1.29, not exceeding 1.5. Sewing test according to GB / T21294-2014: no tearing or pinhole enlargement at the sewing point.

[0089] An example of the mapping between surface roughness Ra and winding parameters (used in Example 1) is shown in Table 1 below.

[0090]

[0091] Table 1

[0092] Example 2

[0093] The difference from Example 1 is that the average particle size of the microcapsules is 1 μm, the amount of nano silica is 5 parts, the dry film thickness of the coating is about 5 μm, and the winding tension is adjusted to 70 N, which corresponds to a fabric with a surface roughness Ra of about 0.15 μm.

[0094] Product performance: Initial vertical burning test: afterflame time 1 second, damaged length 95mm. After 30 washes: damaged length 135mm, acceptable. End face radial misalignment no greater than 2.5mm, number of folds per meter no more than 1.5. Coating surface roughness Ra: 0.15μm. Bending length ratio 1.32, sewing test passed.

[0095] Example 3

[0096] The difference from Example 1 is that the microcapsule wall material is a polyurethane prepolymer instead of melamine resin, the average particle size of the microcapsules is 5 μm, the amount of nano silica in the outer coating slurry is 15 parts, and the winding tension is set to 95 N, which corresponds to a fabric with a surface roughness Ra of about 0.42 μm.

[0097] Product performance: Initial vertical burning test: afterflame time 0 seconds, damaged length 78mm. Damaged length after 30 washes: 105mm. End face radial misalignment no greater than 2mm, no more than 1 fold per meter. Coating surface roughness Ra: 0.42μm. Bending length ratio: 1.25, sewing test passed.

[0098] Example 4

[0099] The difference from Example 1 is that the fabric substrate is a 65:35 polyester-cotton blend woven fabric with a weight of 250 g / m². A hydrogen peroxide bleaching step is added to the pretreatment process, with a hydrogen peroxide concentration of 5 g / L, treated at 80°C for 30 minutes. The amount of microcapsules in the inner working solution is adjusted to 200 parts. The amount of nano-silica in the outer coating slurry is 12 parts. The winding tension is set to 85 N, corresponding to a fabric with a surface roughness Ra of approximately 0.30 μm.

[0100] Product performance: Initial vertical burning test: afterflame time 2 seconds, no dripping, damaged length 120mm. After 30 washes: damaged length 148mm, meeting the requirement of not exceeding 150mm. End face radial misalignment not exceeding 3mm, no more than 2 folds per meter. Coating surface roughness Ra is 0.30μm. Bending length ratio 1.35, passing sewing test.

[0101] Comparative Example 1

[0102] The most traditional process without internal flame-retardant microcapsules, without constant tension winding, and without an outer dense coating.

[0103] I. Pre-processing

[0104] Same pretreatment steps as in Example 1.

[0105] II. Flame-retardant finishing

[0106] A simple padding method was used. The working solution was prepared by adding 200g of commercially available phosphorus-nitrogen flame retardant, 2g of dispersant, and water to a final volume of 1000g, and stirring at high speed for 20 minutes. The phosphorus-nitrogen flame retardant was a non-microencapsulated compound of ammonium polyphosphate, melamine, and pentaerythritol, with an average particle size of approximately 50μm. The pretreated fabric was then padded with the working solution on a two-dip, two-pad mill with a padding rate of 75%, followed by pre-drying at 110℃ for 2 minutes and then baking at 170℃ for 3 minutes.

[0107] III. Regular Coupling

[0108] The flame-retardant treated fabric is wound up using a standard center-drive winding machine without tension detection and adjustment devices, and the winding speed is fixed at 20m / min. During the winding process, the operator manually adjusts the brake, resulting in significant tension fluctuations.

[0109] IV. Volumes

[0110] The 1500-meter roll was manually cut into smaller rolls of 10 meters each, for a total of 150 rolls. The beginning and end of each roll were trimmed to remove wrinkles caused by starting and stopping. On average, each roll was wasted 0.2 meters, for a total wastage of 30 meters. An additional 5 meters was wasted due to trimming caused by uneven fabric surfaces, bringing the total wastage rate to approximately 2.3%.

[0111] Product performance: Afterflame time is 6 seconds under vertical burning method, with molten droplets and a damaged length of 210mm. After 30 washes, the damaged length is 450mm, and the flame retardant performance is completely lost. The radial misalignment at the winding end is 8-15mm, and the number of pleats per meter is 5-8. There is no outer coating, the flame retardant particles are easy to fall off, and the surface sheds powder.

[0112] Comparative Example 2

[0113] It has an inner microcapsule flame-retardant structure but no outer dense coating, and features constant tension winding.

[0114] The difference from Example 1 is that the outer coating construction step is omitted. The constant tension winding parameters are the same as in Example 1, with a tension of 80N. However, due to the lack of a coating, the coefficient of friction on the fabric surface is uneven, resulting in slightly larger actual tension fluctuations, but still within ±5%.

[0115] Product performance: Initial vertical burning test: afterflame time 1 second, damaged length 95mm. After 30 washes: damaged length 340mm, unacceptable. End face radial misalignment no more than 2mm, but the fabric surface is prone to pilling due to lack of coating protection. Uncoated, bending length ratio 1.05, sewing test passed.

[0116] Comparative Example 3

[0117] It has an inner microcapsule flame-retardant structure and an outer dense coating, but it does not have constant tension winding and uses ordinary winding.

[0118] The difference from Example 1 is that the winding method uses a conventional center-driven winding machine with tension-free closed-loop control, and the winding speed is fixed at 30m / min. The remaining steps, including the construction of the inner and outer layers, are the same as in Example 1.

[0119] Product performance: Initial vertical burning test: afterflame time 0 seconds, damaged length 85mm, acceptable. After 30 washes: damaged length 168mm, unacceptable. Due to tension fluctuations during winding, the cured coating was subjected to excessive bending and tensile stress, resulting in microcracks. Scanning electron microscopy confirmed crack widths of 1-3μm. End-face radial misalignment was 8-12mm, with 4-6 pleats per meter. Separation loss rate was approximately 2.1%. Bending length ratio was 1.31. During sewing tests, occasional pinhole enlargement was observed at microcrack locations.

[0120] Comparative Example 4

[0121] It has no inner microcapsule flame-retardant structure, only an outer dense coating, and is wound with constant tension.

[0122] The difference from Example 1 is that the construction step of the inner loose flame-retardant structure is omitted, and a dense coating is directly applied to the outer layer, without adding any flame retardant to the coating slurry. Constant tension winding is the same as in Example 1, with a tension set at 80N.

[0123] Product performance: Initial vertical burning test: afterflame time 18 seconds, molten droplets present and dripping, damaged length 450mm, unacceptable. Damaged length still greater than 450mm after 30 washes, unacceptable. Radial misalignment at the end face not greater than 2mm. Coating integrity good but lacks flame retardant function. Bending length ratio 1.28, sewing test passed.

[0124] The performance summary table is shown in Table 2 below.

[0125]

[0126] Table 2

[0127] Note: The coating integrity evaluation standard uses a scanning electron microscope at 1000x magnification to observe the coating surface. If there are no cracks or pinholes, the coating is considered intact; if cracks with a width ≥1μm are present, it is considered to have microcracks. Bending length is tested according to ASTM D1388, and the ratio is: bending length after coating / bending length of uncoated substrate. Sewing tests are conducted according to GB / T21294-2014.

[0128] Performance Analysis

[0129] As can be seen from the performance summary table, in terms of initial flame retardancy, the damage lengths of Examples 1-4 were 78-120 mm, all superior to the 210 mm of Comparative Example 1 and the greater than 450 mm of Comparative Example 4. Comparative Example 2, which only had an inner layer of microcapsules for flame retardancy without an outer coating, had an initial damage length of 95 mm, similar to the 85 mm of Example 1, indicating that the initial flame retardancy was mainly provided by the inner layer. However, after 30 washes, the damage length of Comparative Example 2 increased sharply to 340 mm, far exceeding the acceptable threshold of 150 mm, while that of Example 1 only increased to 110 mm, still meeting the acceptable standard. Without the protection of a dense outer coating, the flame retardant in the inner microcapsule gradually dissolves during repeated washes, resulting in severely insufficient wash resistance; the outer coating anchors the flame retardant within the fiber through physical sealing, improving flame retardant durability. Comparative Example 3, despite having a complete double-layer structure, used ordinary winding. Fluctuations in winding tension caused micro-cracks in the coating, resulting in a damaged length of 168mm after 30 washes, also failing the test. This demonstrates that coating integrity is crucial for wash resistance. Comparative Example 4 only had an outer coating without an inner flame-retardant layer, resulting in extremely poor flame-retardant performance. The inner microcapsule-like, loose flame-retardant structure provides the primary source of flame retardancy, while the outer continuous, dense coating provides wash-resistant protection. Both are indispensable, and the coating must remain intact and crack-free to effectively provide protection.

[0130] Regarding the neatness of the winding end face, Comparative Example 1, using ordinary winding, had a radial misalignment of 8-15mm, 5-8 pleats per meter, and a winding loss rate of 2.3%. Comparative Example 2, using constant tension winding but without an outer coating, reduced the misalignment to ≤2mm, ≤1 pleat, and a loss rate of 0.5%, indicating that constant tension winding itself can improve winding quality. Example 1, by adding a dense outer coating to constant tension winding, uniformized the fabric friction coefficient, further controlling tension fluctuations from ±5% to within ±3%, resulting in even better end face neatness. Comparative Example 3, although possessing a complete double-layer structure, used ordinary winding, resulting in a misalignment rebounding to 8-12mm, 4-6 pleats, and a loss rate of 2.1%, and more importantly, microcracks appeared in the coating. This indicates that constant tension winding not only determines the winding appearance and loss rate, but also directly relates to the stress distribution of the coating during the winding process: excessive tension fluctuations can cause the cured coating to be subjected to uneven tensile and bending stresses, leading to microcracks and thus compromising flame retardant durability. Examples 1-3 demonstrate that by adjusting the set tension using a pre-stored tension-speed mapping table under different surface roughnesses, excellent end-face quality and intact coatings were obtained in all cases. Regarding the bending length ratio, all examples were no greater than 1.5, indicating that the outer coating did not significantly sacrifice the fabric's softness; in the sewing test, only Comparative Example 3 showed pinhole enlargement due to microcracks, while the others were qualified. In summary, the three elements of inner microcapsule flame retardancy, outer dense coating, and constant tension winding form a complete synergistic chain: the inner layer provides flame retardancy, the outer layer protects the inner layer and homogenizes the surface friction coefficient, and constant tension winding protects the coating integrity while ensuring high-stability winding. The absence of any single element will lead to at least one key performance failure; only when all three are present can the unity of low slitting loss, high winding stability, coating integrity, and flame retardant durability be achieved.

[0131] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a low-loss flame-retardant curtain fabric, characterized in that, Includes the following steps: The fabric substrate is treated with flame retardant to form a double-layer flame retardant structure consisting of an inner loose flame retardant structure and an outer continuous dense flame retardant coating. The flame-retardant treated fabric is wound up using a constant tension winding device, which includes a tension detection unit and a tension adjustment unit. The tension detection unit is used to detect the tension value of the fabric during the winding process in real time, and the tension adjustment unit automatically adjusts the winding speed or braking torque according to the detected tension value to keep the fabric tension constant during the winding process. The large roll of fabric formed by constant tension winding is cut into multiple smaller rolls; Among them, the outer continuous dense flame-retardant coating makes the friction coefficient of the fabric surface uniform, thereby improving the stability of constant tension winding and the neatness of the end face; Meanwhile, constant tension winding reduces fabric wrinkles and stress concentration, ensuring that the outer continuous and dense flame-retardant coating remains intact after curing.

2. The method for preparing a low-loss flame-retardant curtain fabric according to claim 1, characterized in that: Flame retardant finishing specifically includes: Steps for constructing the inner layer of fluffy flame retardant structure: Impregnate the fabric substrate with a working liquid containing phosphorus and nitrogen-based intumescent flame retardant, then dry it at 100℃-120℃ for 3-5 minutes, and then bake it at 150℃-170℃ for 1-3 minutes to allow the flame retardant to adhere to the fabric surface and fiber gaps, forming a fluffy, stacked inner layer flame retardant structure. Construction steps of the outer continuous dense flame retardant coating: A coating slurry containing water-based polyurethane resin, nano silica and crosslinking agent is coated on the inner flame retardant structure, and then dried and cured to form a continuous dense flame retardant coating without pinholes. The coating slurry comprises, by weight: 100 parts waterborne polyurethane resin, 5-15 parts nano silica, 2-5 parts crosslinking agent, 0.1-0.5 parts dispersant, and 0.1-0.3 parts defoamer.

3. The method for preparing a low-loss flame-retardant curtain fabric according to claim 2, characterized in that: The phosphorus-nitrogen intumescent flame retardant is added in the form of microcapsules. The core material of the microcapsules is a compound of ammonium polyphosphate, melamine and pentaerythritol, and the wall material is melamine resin. The average particle size of the microcapsules is 1μm-5μm.

4. The method for preparing a low-loss flame-retardant curtain fabric according to claim 2, characterized in that: The outer continuous dense flame-retardant coating has a dry film thickness of 5μm-20μm, the nano-silica has a particle size of 10nm-20nm, and the coating slurry does not contain phosphorus-based flame retardants.

5. The method for preparing a low-loss flame-retardant curtain fabric according to claim 1, characterized in that: The tension detection unit includes a floating roller and a displacement sensor. The displacement sensor is a non-contact sensor. It detects the displacement of the floating roller and calculates the real-time tension value of the fabric based on the displacement-tension calibration curve. The tension adjustment unit achieves constant tension by adjusting the rotational speed of the take-up roller or the output torque of the take-up motor.

6. The method for preparing a low-loss flame-retardant curtain fabric according to claim 5, characterized in that: Non-contact displacement sensors are laser displacement sensors or ultrasonic displacement sensors.

7. The method for preparing a low-loss flame-retardant curtain fabric according to claim 1, characterized in that: The constant tension winding device is also equipped with a non-stop winding mechanism that automatically switches to an empty core when the winding reaches the set length, so as to achieve continuous winding and eliminate end face wrinkles and head and tail waste caused by stopping and starting. Furthermore, in the step of cutting into small rolls, the length of each small roll is set to be no less than 5 meters.

8. A low-loss flame-retardant curtain fabric, prepared by the method described in any one of claims 1-7, characterized in that, include: The curtain roll includes a fabric substrate, an inner fluffy flame-retardant structure distributed on the surface of the fabric substrate and in the fiber gaps, and an outer continuous dense flame-retardant coating covering at least one outer surface. The radial misalignment between adjacent layers on the small roll end of the curtain fabric roll shall not exceed 3mm, and the number of obvious creases on the fabric surface caused by uneven rolling pressure or tension fluctuations per meter length shall not exceed 2. After the curtain roll is washed 30 times according to the washing procedure specified in GB / T17591, the damaged length measured by the vertical burning method shall not exceed 150mm.

9. A low-loss flame-retardant curtain fabric according to claim 8, characterized in that: The outer continuous dense flame-retardant coating has no pinholes, and the bending length measured according to ASTM D1388 standard is no more than 1.5 compared with the uncoated fabric substrate of the same batch. When conducting a sewing test according to GB / T21294-2014 standard, there should be no tearing or enlargement of the needle hole at the sewing point.

10. A low-loss flame-retardant curtain fabric according to claim 8, characterized in that: The surface arithmetic mean roughness Ra of the outer continuous dense flame-retardant coating is 0.1μm-0.5μm, and the tension adjustment unit of the constant tension winding device stores a tension-speed mapping table that matches this roughness range.

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