Halogen-free flame-retardant industrial paper tube base paper and preparation method thereof

Abstract

The application discloses a halogen-free flame-retardant industrial paper tube base paper and a preparation method thereof. The paper tube base paper is based on the total mass of the absolute dry fibers and comprises the following components by mass: waste carton board paper fibers 65-75 parts, coniferous wood long fibers 10-15 parts, halogen-free phosphorus-nitrogen-silicon composite flame retardant 4-7 parts, fiber cross-linking reinforcing agent 1.2-2.0 parts, amphoteric starch sizing agent 3-5 parts, nano-silicon dioxide moisture-proof modifier 0.8-1.5 parts, and polyacrylamide retention agent 0.2-0.5 parts. Through the synergistic effect of the four processes of gradient beating, medium-temperature in-situ cross-linking, double-sided differential sizing and segmented gradient drying on the basis of the above ingredients, the paper tube base paper not only has good flame-retardant performance, but also has increased tensile strength and ring crush index of the paper, improves the paper strength, and has bonding adaptation, moisture resistance and storage resistance, so that the integration of the four functions of the paper tube base paper is improved.

Description

Technical Field

[0001] This invention belongs to the field of papermaking technology, and particularly relates to a halogen-free flame-retardant industrial paper tube base paper and its preparation method. Background Technology

[0002] Industrial paper tubes are widely used in industries such as film, chemical fiber, paper, metal coils, and fire-fighting storage. Ordinary paper tube base paper is made from pure plant fibers and is highly flammable, posing a fire hazard under conditions such as high-temperature production, enclosed storage, and high-speed friction. To meet industrial fire protection requirements, various flame-retardant paper tube base papers have emerged on the market, but existing products still have many shortcomings:

[0003] On the one hand, many flame-retardant paper tube base papers use halogenated flame retardants or single phosphorus-based flame retardants. Halogenated flame retardants release toxic and harmful gases when burning, which does not meet environmental protection requirements; single phosphorus-based flame retardants often only physically adsorb onto the fiber surface, and are prone to migration and precipitation after long-term storage or exposure to moisture, resulting in powdering and whitening (i.e., the flame retardant precipitates from the fiber surface to form a white powdery substance, causing the paper surface to turn white), leading to a rapid decline in flame retardant performance and a lack of long-lasting flame retardancy in the product.

[0004] On the other hand, the excessive use of flame retardants can damage the bonding between fibers, resulting in a significant decrease in the ring crush strength and tensile strength of the base paper. This makes the paper tubes prone to deformation, delamination, and chipping after winding, failing to meet industrial load-bearing requirements. Furthermore, the damaged pore structure of the flame-retardant modified paper leads to poor compatibility with special white glue and starch glue for paper tubes, resulting in uneven glue absorption, weak adhesion, and later delamination. Traditional processes often employ single-sided flame-retardant impregnation, which has poor moisture resistance; moisture intrusion accelerates the deactivation of the flame-retardant components.

[0005] In summary, existing technologies struggle to simultaneously achieve a balance of properties such as halogen-free environmental friendliness, long-lasting flame retardancy, high strength, good adhesion, and moisture resistance. There is an urgent need for a flame-retardant industrial paper tube base paper preparation technology that can achieve a balance of these properties and is suitable for industrial mass production. Summary of the Invention

[0006] In view of the above-mentioned defects in the prior art, the technical problem to be solved by the present invention is to provide a halogen-free flame-retardant industrial paper tube base paper that is not only halogen-free and environmentally friendly, but also has comprehensive properties such as long-lasting flame retardancy, high strength, good adhesion and moisture resistance.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A halogen-free flame-retardant industrial paper tube base paper, based on the total dry fiber mass, comprises the following raw material components in parts by mass:

[0009] The composition includes 65-75 parts waste cardboard fiber, 10-15 parts long coniferous fiber, 4-7 parts halogen-free phosphorus-nitrogen-silicon composite flame retardant, 1.2-2.0 parts fiber crosslinking reinforcing agent, 3-5 parts amphoteric starch sizing agent, 0.8-1.5 parts nano silica moisture-proof modifier, and 0.2-0.5 parts polyacrylamide retention aid.

[0010] Preferably, the beating degree of the waste paperboard fiber is 38-42°SR.

[0011] Preferably, the beating degree of the coniferous long fibers is 45-48°SR.

[0012] Preferably, the halogen-free phosphorus-nitrogen-silicon composite flame retardant comprises ammonium polyphosphate, melamine, and nano-organic silicon, mixed in a mass ratio of 5:2:1; the nano-organic silicon is an organosilicon sol with a particle size of 20-50 nm.

[0013] Preferably, the fiber crosslinking reinforcing agent comprises carboxymethyl cellulose and an epoxy crosslinking agent, which are mixed in a mass ratio of 1:1 to 2:1.

[0014] Preferably, the particle size of the nano-silica moisture-proof modifier is 30-60 nm.

[0015] Preferably, the base paper includes a paper blank, and a hydrophilic adhesive layer and a hydrophobic flame-retardant and moisture-proof layer are respectively provided on both sides of the paper blank. The hydrophilic adhesive layer is formed by applying an amphoteric starch sizing agent to one side of the paper blank; the hydrophobic flame-retardant and moisture-proof layer is formed by applying an amphoteric starch sizing agent and a nano-silica moisture-proof modifier to the other side of the paper blank.

[0016] Preferably, the epoxy crosslinking agent is polyamide epichlorohydrin resin.

[0017] Preferably, the longitudinal ring crush index of the base paper is ≥8.5 N·m / g, the transverse tensile strength is ≥4.2 kN / m, the vertical flammability rating reaches UL94V-0, and there is no powdering or whitening after 6 months of storage at room temperature, and the flame retardant performance does not decrease.

[0018] Based on the same inventive concept, another technical problem solved by this invention is to provide a method for preparing halogen-free flame-retardant industrial paper tube base paper. The prepared industrial paper tube base paper is not only halogen-free and environmentally friendly, but also has comprehensive properties such as long-lasting flame retardancy, high strength, good adhesion and moisture resistance.

[0019] A method for preparing the above-mentioned halogen-free flame-retardant industrial paper tube base paper includes the following steps:

[0020] S1. Fiber pulp compounding: Waste cardboard fiber and softwood long fiber are put into the pulping tank, deionized water is added and stirred evenly to prepare a mixed fiber pulp with a solid content of 3.5-4.5%.

[0021] S2. In-slurry modification and flame retardant treatment: Add fiber crosslinking reinforcing agent and polyacrylamide retention aid to the mixed fiber slurry in sequence, and stir at 280-320 r / min for 5-8 min; then add halogen-free phosphorus-nitrogen-silicon composite flame retardant, heat to 55-60℃ and stir at a constant temperature for 15-20 min to allow the flame retardant to undergo an in-situ crosslinking reaction with the fiber, and obtain the modified slurry;

[0022] S3. Papermaking: The modified pulp is dewatered and pressed through the wire section to form a paper blank, and the moisture content of the wet paper is controlled at 40-45%.

[0023] S4. Double-sided differentiation: A double-sided roller coating process is adopted, with a solution containing amphoteric starch sizing agent coated on the front side of the paper blank and a solution containing amphoteric starch sizing agent and nano-silica moisture-proof modifier coated on the back side of the paper blank.

[0024] S5. Segmented Drying and Shaping: A gradient temperature drying process is adopted. The first stage is pre-drying at 70-75℃ for 3-5 minutes, and the second stage is high-temperature curing at 90-95℃ for 8-12 minutes to allow the flame retardant to cross-link and cure in situ. After cooling and humidifying to a moisture content of 6.0-8.0% for the finished paper, it is then calendered and slit to obtain the finished product.

[0025] After adopting the above technical solution, the beneficial effects of the present invention are:

[0026] This invention relates to a halogen-free flame-retardant industrial paper tube base paper made from waste cardboard fiber and softwood long fiber, combined with a halogen-free phosphorus-nitrogen-silicon composite flame retardant composed of ammonium polyphosphate, melamine, and nano-organic silicon in a mass ratio of 5:2:1, and a fiber crosslinking reinforcing agent composed of carboxymethyl cellulose and polyamide epichlorohydrin resin in a mass ratio of 1:1 to 2:1. Through gradient pulping and compounding of long and short fibers, the longitudinal tensile strength and ring crush bearing capacity of the base paper are synergistically improved. The aforementioned halogen-free phosphorus-nitrogen-silicon composite flame retardant utilizes the synergistic effect of phosphorus-based char promotion, nitrogen-based flame retardancy and smoke suppression, and silicon-based moisture protection to achieve highly efficient halogen-free flame retardancy; the aforementioned fiber crosslinking reinforcing agent constructs a chemical bond network, which not only compensates for strength loss but also improves the bonding stability between the flame-retardant components and the fibers. Based on the above ingredients, through the synergistic effect of four major processes—gradient pulping, medium-temperature in-situ crosslinking, double-sided differentiated sizing, and segmented gradient drying—the paper tube base paper not only has good flame retardant properties, but also increases the tensile strength and ring crush index, improving the paper strength. Furthermore, it is compatible with adhesives, moisture-proof, and durable, thus achieving an integrated enhancement of the four functions of the paper tube base paper.

[0027] The base paper prepared by the above-mentioned method for preparing halogen-free flame-retardant industrial paper tube base paper is not only halogen-free and environmentally friendly, but also has a longitudinal ring crush index ≥8.5 N·m / g, a transverse tensile strength ≥4.2 kN / m, a flame retardant rating of UL94V-0, and no powdering or whitening after 6 months of storage at room temperature. It also has a strong bond with paper tube white glue and starch glue, making it suitable for industrial flame-retardant paper tube scenarios such as high-temperature working conditions, warehouse fire prevention, and roll winding. The preparation process is compatible with existing paper production lines. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention.

[0029] This invention provides a halogen-free flame-retardant industrial paper tube base paper, based on the total dry fiber mass, comprising the following raw material components in parts by weight: 65-75 parts waste cardboard fiber, 10-15 parts long softwood fiber, 4-7 parts halogen-free phosphorus-nitrogen-silicon composite flame retardant, 1.2-2.0 parts fiber crosslinking reinforcing agent, 3-5 parts amphoteric starch sizing agent, 0.8-1.5 parts nano-silica moisture-proof modifier, and 0.2-0.5 parts polyacrylamide retention aid. The waste cardboard fiber and long softwood fiber are mixed in the above-mentioned parts by weight. This blending of long and short fibers not only ensures paper quality but is also environmentally friendly and cost-effective. The reasons are as follows: waste cardboard is low in cost and environmentally friendly. However, after multiple recycling processes, the fibers in waste cardboard undergo "keratinization," becoming short, thick, and stiff, and the bonding strength between fibers decreases significantly. If only waste paper pulp is used, the ring crush strength and bursting strength of the paper tube base paper are often insufficient, making it prone to breakage during winding. The long and flexible coniferous wood fibers, when added in quantities of 10-15 parts, interweave like a skeleton within the short fibers of waste paper. This mixture significantly improves the paper's folding endurance and interlayer bonding strength, ensuring that the paper tube does not crack under high-speed winding and heavy pressure. This not only makes environmentally friendly use of waste cardboard but also compensates for the paper's quality deficiencies through the long coniferous wood fibers.

[0030] Preferably, the freeness of the waste paperboard fiber is 38–42°SR, and the freeness of the softwood long fiber is 45–48°SR. This gradient beating and blending of long and short fibers improves the longitudinal tensile strength and ring crush resistance of the base paper.

[0031] In some embodiments, the halogen-free phosphorus-nitrogen-silicon composite flame retardant comprises ammonium polyphosphate, melamine, and nano-organosilicon, mixed in a mass ratio of 5:2:1; the nano-organosilicon is an organosilicon sol with a particle size of 20-50 nm. Utilizing the synergistic effect of phosphorus-based char promotion, nitrogen-based flame retardancy and smoke suppression, and silicon-based moisture protection, highly efficient halogen-free flame retardancy of the base paper is achieved, while simultaneously improving the bonding stability between the flame retardant components and the fibers.

[0032] In some embodiments, the fiber crosslinking reinforcing agent comprises carboxymethyl cellulose and an epoxy crosslinking agent, mixed in a mass ratio of 1:1 to 2:1. This effectively repairs fiber gaps caused by flame retardant filling, significantly improves paper ring crush and tensile properties, and resolves the conflict between flame retardancy and strength.

[0033] Preferably, the particle size of the nano-silica moisture-proof modifier is 30-60 nm.

[0034] It should be noted that in this invention, "nano-organic silicon" specifically refers to the organosilicon sol used as one of the components of the halogen-free phosphorus-nitrogen-silicon composite flame retardant. This component is added to the slurry along with the composite flame retardant, playing a synergistic role in flame retardancy and moisture protection within the slurry. "Nano-silica" specifically refers to the inorganic nanoparticles used to construct a hydrophobic barrier in the back sizing layer, forming a moisture-proof layer on the surface of the paper blank. The two have different chemical compositions, addition methods, and functions, and are not interchangeable.

[0035] Halogen-free flame-retardant industrial paper tube base paper includes a paper blank, with a hydrophilic adhesive layer and a hydrophobic flame-retardant and moisture-proof layer on both sides of the paper blank, forming a double-sided differentiated functional structure. The hydrophilic adhesive layer is formed by coating an amphoteric starch sizing agent on one side of the paper blank; the hydrophobic flame-retardant and moisture-proof layer is formed by coating an amphoteric starch sizing agent and a nano-silica moisture-proof modifier on the other side of the paper blank.

[0036] The present invention provides a hydrophilic adhesive layer and a hydrophobic flame-retardant moisture-proof layer on both sides of the paper blank of the halogen-free flame-retardant industrial paper tube base paper, forming a double-sided differentiated functional structure. The bonding surface of the paper tube is a hydrophilic adhesive layer, which is formed by applying an amphoteric starch sizing agent to one side of the paper blank, retaining the activity of fiber pores, ensuring uniform penetration of white glue and starch glue, and strong adhesion; the other side is provided with a hydrophobic flame-retardant moisture-proof layer, which is formed by applying an amphoteric starch sizing agent and a nano-silica moisture-proof modifier to the other side of the paper blank. The hydrophobic flame-retardant moisture-proof layer can block external moisture, lock in the internal flame-retardant components, and prevent moisture-induced failure, powdering, and whitening problems.

[0037] In some embodiments, the epoxy crosslinking agent is a polyamide epichlorohydrin resin.

[0038] The halogen-free flame-retardant industrial paper tube base paper of this invention has a longitudinal ring crush index ≥8.5 N·m / g, a transverse tensile strength ≥4.2 kN / m, a vertical flammability rating of UL94V-0, and exhibits no powdering or whitening after 6 months of storage at room temperature with no degradation in flame-retardant performance.

[0039] This invention provides a method for preparing halogen-free flame-retardant industrial paper tube base paper as described above, comprising the following steps:

[0040] S1. Fiber pulp compounding: Waste cardboard fiber and softwood long fiber are put into the pulping tank, deionized water is added and stirred evenly to prepare a mixed fiber pulp with a solid content of 3.5-4.5%; the above-mentioned waste cardboard fiber is 65-75 parts, preferably with a freeness of 38-42°SR; softwood long fiber is 10-15 parts, preferably with a freeness of 45-48°SR;

[0041] S2. In-situ modification and flame retardant treatment: Add 1.2-2.0 parts of fiber crosslinking reinforcing agent and 0.2-0.5 parts of polyacrylamide retention aid to the mixed fiber slurry in sequence, and stir at 280-320 r / min for 5-8 min; then add 4-7 parts of halogen-free phosphorus-nitrogen-silicon composite flame retardant, heat to 55-60℃ and stir at a constant temperature for 15-20 min to allow the flame retardant to undergo an in-situ crosslinking reaction with the fiber, and obtain the modified slurry;

[0042] The fiber crosslinking reinforcing agent and polyacrylamide retention aid are added sequentially in steps, with a stirring interval of no less than 3 minutes after each addition of the agent.

[0043] S3. Papermaking: The modified pulp is dewatered and pressed through the wire section to form a paper blank, and the moisture content of the wet paper is controlled at 40-45%.

[0044] S4. Double-sided Differentiation: A double-sided roller coating process is used. A hydrophilic adhesive layer is formed by coating the front side of the paper blank with a solution containing an amphoteric starch sizing agent. This solution is typically formed by mixing deionized water and the amphoteric starch sizing agent, with a mass concentration of 8–10% and a coating weight of 8–10 g / m². A hydrophobic, flame-retardant, and moisture-proof layer is formed by coating the back side of the paper blank with a solution containing an amphoteric starch sizing agent and a nano-silica moisture-proof modifier. Preferably, the nano-silica moisture-proof modifier has a particle size of 30–60 nm. This solution is typically formed by mixing deionized water with the amphoteric starch sizing agent and the nano-silica moisture-proof modifier, with a solid content of 10–12% and a coating weight of 6–8 g / m².

[0045] In this invention, 'coating amount' refers to the dry weight of the coating remaining on a unit area of ​​paper blank after coating and drying, and its value is measured by weighing method (i.e., the difference in mass of the dry paper sample before and after coating divided by the area).

[0046] S5. Segmented drying and shaping: A gradient temperature drying process is adopted. The first stage is pre-drying at 70-75℃ for 3-5 minutes, and the second stage is high-temperature curing at 90-95℃ for 8-12 minutes to allow the halogen-free phosphorus-nitrogen-silicon composite flame retardant to crosslink and cure in situ. After cooling and humidifying to the moisture content of the finished paper at 6.0-8.0%, it is then calendered and slit to obtain the finished product.

[0047] This invention achieves a synergistic enhancement of four functions—flame retardancy, reinforcement, adhesive compatibility, and moisture resistance—through the combined effects of four processes: gradient pulping, medium-temperature in-situ crosslinking, double-sided differentiated sizing, and segmented gradient drying. These processes are not simply superimposed but rather work in tandem: gradient pulping provides the fiber morphology basis for crosslinking reinforcement; medium-temperature in-situ crosslinking enables the flame retardant to form chemical bonds with the fibers; double-sided differentiated sizing ensures internal adhesion while building an external moisture barrier; and segmented gradient drying ensures deep curing of the flame retardant components without damaging the paper structure. The absence of any single process would lead to a significant deterioration in overall performance.

[0048] The technical solutions in the embodiments of this application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this invention.

[0049] Example 1

[0050] A halogen-free flame-retardant industrial paper tube base paper, based on the total dry fiber mass, is prepared from the following raw materials in parts by weight:

[0051] Waste cardboard fiber content: 68 parts; beating degree: 40°SR.

[0052] 14 parts of long coniferous fiber, with a freeness of 48°SR;

[0053] 5.5 parts of halogen-free phosphorus-nitrogen-silicon composite flame retardant;

[0054] 1.2 parts of fiber crosslinking reinforcing agent;

[0055] 4.5 parts of amphoteric starch sizing agent;

[0056] 1.5 parts of nano-silica moisture-proof modifier, with a particle size of 30nm;

[0057] 0.4 parts of polyacrylamide retention aid; wherein, the halogen-free phosphorus-nitrogen-silicon composite flame retardant is composed of ammonium polyphosphate, melamine, and nano-organic silica in a mass ratio of 5:2:1; the nano-organic silica is an organosilicone sol with a particle size of 30nm. The fiber crosslinking reinforcing agent includes carboxymethyl cellulose and epoxy crosslinking agent, which are mixed in a mass ratio of 1:1. The preparation steps are as follows:

[0058] S1. Fiber pulp compounding: Waste cardboard fiber and softwood long fiber are put into the pulping tank, deionized water is added and stirred evenly to prepare a mixed fiber pulp with a solid content of 4.0%.

[0059] S2. In-slurry modification and flame retardant treatment: Fiber crosslinking reinforcing agent and polyacrylamide retention aid are added sequentially to the mixed fiber slurry and stirred at 300 r / min for 6 min; then halogen-free phosphorus-nitrogen-silicon composite flame retardant is added, and the temperature is raised to 58℃ and stirred for 17 min to allow the flame retardant components to undergo an in-situ crosslinking reaction with the fibers, thus obtaining the modified slurry; the stirring interval after each addition of the additive is 4 min.

[0060] S3. Papermaking: The modified pulp is dewatered and pressed through the wire section to form a paper blank, and the moisture content of the wet paper is controlled at 42%.

[0061] S4. Double-sided Differentiation: A double-sided roller coating process is used. The front side of the paper blank is coated with a solution containing an amphoteric starch sizing agent. This solution is typically formed by mixing deionized water and the amphoteric starch sizing agent, resulting in a 9% (w / w) amphoteric starch sizing agent solution with a coating weight of 10 g / m². The back side of the paper blank is coated with a solution containing both the amphoteric starch sizing agent and a nano-silica moisture-proof modifier. Preferably, the nano-silica moisture-proof modifier has a particle size of 30 nm. This solution is typically formed by mixing deionized water with the amphoteric starch sizing agent and the nano-silica moisture-proof modifier, with a solid content of 11% and a coating weight of 7 g / m².

[0062] S5. Segmented drying and shaping: A gradient temperature drying process is adopted. The first stage is pre-drying at 72℃ for 4 minutes, and the second stage is high-temperature curing at 92℃ for 10 minutes to allow the halogen-free phosphorus-nitrogen-silicon composite flame retardant to cross-link and cure in situ. After cooling and humidifying to a moisture content of 7.0% for the finished paper, it is then calendered and slit to obtain the finished product.

[0063] The halogen-free flame-retardant industrial paper tube base paper prepared in this embodiment has a hydrophilic adhesive layer on one side and a hydrophobic flame-retardant and moisture-proof layer on the other side. The ring crush index was tested according to GB / T2679.8, the tensile strength according to GB / T12914, and the flame retardancy rating according to the UL94 vertical burning method. The longitudinal ring crush index is 9.1 N·m / g, the transverse tensile strength is 4.8 kN / m, and the flame retardancy rating is UL94V-0. After 6 months of storage at room temperature, there was no powdering or whitening, and the paper tube adhered firmly to the white adhesive without delamination.

[0064] Example 2

[0065] A halogen-free flame-retardant industrial paper tube base paper, based on the total dry fiber mass, is prepared from the following raw materials in parts by weight:

[0066] 72 parts of waste cardboard fiber, with a beating degree of 40°SR;

[0067] 11 parts of long coniferous fiber, with a freeness of 46°SR;

[0068] Four parts of halogen-free phosphorus-nitrogen-silicon composite flame retardant;

[0069] 2.0 parts of fiber crosslinking reinforcing agent;

[0070] 3.5 parts of amphoteric starch sizing agent;

[0071] 1.2 parts of nano-silica moisture-proof modifier, with a particle size of 60nm;

[0072] 0.3 parts of polyacrylamide retention aid;

[0073] The halogen-free phosphorus-nitrogen-silicon composite flame retardant is composed of ammonium polyphosphate, melamine, and nano-organic silica in a mass ratio of 5:2:1; the nano-organic silica is an organosilicon sol with a particle size of 30 nm. The fiber crosslinking reinforcing agent includes carboxymethyl cellulose and an epoxy crosslinking agent, mixed in a mass ratio of 1.5:1. The preparation steps are as follows:

[0074] S1. Fiber pulp compounding: Waste cardboard fiber and softwood long fiber are put into the pulping tank, deionized water is added and stirred evenly to prepare a mixed fiber pulp with a solid content of 4.0%.

[0075] S2. In-slurry modification and flame retardant treatment: Fiber crosslinking reinforcing agent and polyacrylamide retention aid are added sequentially to the mixed fiber slurry and stirred at 300 r / min for 6 min; then halogen-free phosphorus-nitrogen-silicon composite flame retardant is added, and the temperature is raised to 60℃ and stirred for 15 min to allow the flame retardant components to undergo in-situ crosslinking reaction with the fibers, thus obtaining the modified slurry; the stirring interval after each addition of the additive is 4 min.

[0076] S3. Papermaking: The modified pulp is dewatered and pressed through the wire section to form a paper blank, and the moisture content of the wet paper is controlled at 42%.

[0077] S4. Double-sided Differentiation: A double-sided roller coating process is used. The front side of the paper blank is coated with a solution containing an amphoteric starch sizing agent. This solution is typically formed by mixing deionized water and the amphoteric starch sizing agent, resulting in a 9% (w / w) amphoteric starch sizing agent solution with a coating weight of 8 g / m². The back side of the paper blank is coated with a solution containing an amphoteric starch sizing agent and a nano-silica moisture-proof modifier. Preferably, the nano-silica moisture-proof modifier has a particle size of 60 nm. This solution is typically formed by mixing deionized water with the amphoteric starch sizing agent and the nano-silica moisture-proof modifier, with a solid content of 11% and a coating weight of 6 g / m².

[0078] S5. Segmented drying and shaping: A gradient temperature drying process is adopted. The first stage is pre-drying at 72℃ for 4 minutes, and the second stage is high-temperature curing at 92℃ for 10 minutes to allow the halogen-free phosphorus-nitrogen-silicon composite flame retardant to cross-link and cure in situ. After cooling and humidifying to a moisture content of 7.0% for the finished paper, it is then calendered and slit to obtain the finished product.

[0079] The halogen-free flame-retardant industrial paper tube base paper prepared in this embodiment has a hydrophilic adhesive layer on one side and a hydrophobic flame-retardant and moisture-proof layer on the other side. The ring crush index was tested according to GB / T2679.8, the tensile strength according to GB / T12914, and the flame retardancy rating according to the UL94 vertical burning method. The longitudinal ring crush index is 8.7 N·m / g, the transverse tensile strength is 4.4 kN / m, and the flame retardancy rating is UL94V-0. After 6 months of storage at room temperature, there was no powdering or whitening, and the paper tube adhered firmly to the white adhesive without delamination.

[0080] Example 3

[0081] A halogen-free flame-retardant industrial paper tube base paper, based on the total dry fiber mass, is prepared from the following raw materials in parts by weight:

[0082] 70 parts waste cardboard fiber, beating degree 40°SR;

[0083] 12 parts of long coniferous fiber, with a freeness of 46°SR;

[0084] 7 parts of halogen-free phosphorus-nitrogen-silicon composite flame retardant;

[0085] 1.6 parts of fiber crosslinking reinforcing agent;

[0086] 4 parts of amphoteric starch sizing agent;

[0087] 0.8 parts of nano-silica moisture-proof modifier, with a particle size of 45nm;

[0088] 0.3 parts of polyacrylamide retention aid;

[0089] The halogen-free phosphorus-nitrogen-silicon composite flame retardant is composed of ammonium polyphosphate, melamine, and nano-organic silicon in a mass ratio of 5:2:1; the nano-organic silicon is an organosilicone sol with a particle size of 30nm; the fiber crosslinking reinforcing agent includes carboxymethyl cellulose and epoxy crosslinking agent, which are mixed in a mass ratio of 2:1; the preparation steps are as follows:

[0090] S1. Fiber pulp compounding: Waste cardboard fiber and softwood long fiber are put into the pulping tank, deionized water is added and stirred evenly to prepare a mixed fiber pulp with a solid content of 4.0%.

[0091] S2. In-slurry modification and flame retardant treatment: Fiber crosslinking reinforcing agent and polyacrylamide retention aid are added sequentially to the mixed fiber slurry and stirred at 300 r / min for 6 min; then halogen-free phosphorus-nitrogen-silicon composite flame retardant is added, and the temperature is raised to 55℃ and stirred for 20 min to allow the flame retardant components to undergo an in-situ crosslinking reaction with the fibers, thus obtaining the modified slurry; the stirring interval after each addition of the additive is 4 min.

[0092] S3. Papermaking: The modified pulp is dewatered and pressed through the wire section to form a paper blank, and the moisture content of the wet paper is controlled at 42%.

[0093] S4. Double-sided Differentiation: A double-sided roller coating process is used. The front side of the paper blank is coated with a solution containing an amphoteric starch sizing agent. This solution is typically formed by mixing deionized water and the amphoteric starch sizing agent, resulting in a 9% (w / w) amphoteric starch sizing agent solution with a coating weight of 9 g / m². The back side of the paper blank is coated with a solution containing an amphoteric starch sizing agent and a nano-silica moisture-proof modifier. Preferably, the nano-silica moisture-proof modifier has a particle size of 45 nm. This solution is typically formed by mixing deionized water with the amphoteric starch sizing agent and the nano-silica moisture-proof modifier, with a solid content of 11% and a coating weight of 8 g / m².

[0094] S5. Segmented drying and shaping: A gradient temperature drying process is adopted. The first stage is pre-drying at 72℃ for 4 minutes, and the second stage is high-temperature curing at 92℃ for 10 minutes to allow the halogen-free phosphorus-nitrogen-silicon composite flame retardant to cross-link and cure in situ. After cooling and humidifying to a moisture content of 7.0% for the finished paper, it is then calendered and slit to obtain the finished product.

[0095] The halogen-free flame-retardant industrial paper tube base paper prepared in this embodiment has a hydrophilic adhesive layer on one side and a hydrophobic flame-retardant and moisture-proof layer on the other side. The ring crush index was tested according to GB / T2679.8, the tensile strength according to GB / T12914, and the flame retardancy rating according to the UL94 vertical burning method. The longitudinal ring crush index is 9.3 N·m / g, the transverse tensile strength is 5.0 kN / m, and the flame retardancy rating is UL94V-0. After 6 months of storage at room temperature, there was no powdering or whitening, and the paper tube adhered firmly to the white adhesive without delamination.

[0096] Comparative Example 1

[0097] This comparative example deliberately removes some key process features of the present invention, retaining the basic formula for conventional preparation. Specifically, refer to the raw material ratios and preparation method of Example 1, with the only difference being:

[0098] The beating degree of waste cardboard fiber and softwood long fiber is uniformly 42°SR, and gradient beating is not used;

[0099] The ring crush index of the obtained base paper was tested according to GB / T2679.8, the tensile strength according to GB / T12914, and the flame retardancy rating according to the UL94 vertical burning method: longitudinal ring crush index 7.8 N·m / g, transverse tensile strength 4.0 kN / m, flame retardancy rating UL94V-0. After 6 months of storage at room temperature, slight powdering and whitening occurred, and the paper tube was firmly bonded to the white glue without delamination.

[0100] Comparative Example 2

[0101] This comparative example deliberately removes some key process features of the present invention, retaining the basic formula for conventional preparation. Specifically, refer to the raw material ratios and preparation method of Example 1, with the only difference being:

[0102] No fiber crosslinking reinforcing agent added;

[0103] The obtained base paper was tested according to GB / T2679.8 for ring crush index, GB / T12914 for tensile strength, and UL94 vertical burning method for flame retardancy rating: longitudinal ring crush index 6.5 N·m / g, transverse tensile strength 3.3 kN / m, flame retardancy rating UL94V-0. After 6 months of storage at room temperature, there was obvious powdering and whitening, and slight delamination of the white glue bonded to the paper tube.

[0104] Comparative Example 3

[0105] This comparative example deliberately removes some key process features of the present invention, retaining the basic formula for conventional preparation. Specifically, refer to the raw material ratios and preparation method of Example 1, with the only difference being:

[0106] The flame retardant is replaced with an equal amount of monoammonium polyphosphate, and the flame retardant treatment in the slurry is carried out at room temperature (25℃), without in-situ crosslinking reaction at 55-60℃;

[0107] The resulting base paper was tested according to GB / T2679.8 for ring crush index, GB / T12914 for tensile strength, and UL94 for flame retardancy rating: longitudinal ring crush index 7.5 N·m / g, transverse tensile strength 3.8 kN / m, flame retardancy rating not specified (smoldering). After 6 months of storage at room temperature, severe powdering and obvious whitening occurred. The paper adhered firmly to the white glue on the paper tube without delamination.

[0108] Comparative Example 4

[0109] This comparative example deliberately removes some key process features of the present invention, retaining the basic formula for conventional preparation. Specifically, refer to the raw material ratios and preparation method of Example 1, with the only difference being:

[0110] Only the front side of the paper blank is sizing with amphoteric starch (sizing amount 9g / ㎡), and the back side is not treated with hydrophobic and moisture-proof sizing.

[0111] The resulting base paper was tested according to GB / T2679.8 for ring crush index, GB / T12914 for tensile strength, and UL94 vertical burning method for flame retardancy rating: longitudinal ring crush index 8.5 N·m / g, transverse tensile strength 4.7 kN / m, flame retardancy test no rating (smoldering), after 6 months of storage at room temperature, obvious powdering and local whitening appeared, and the white glue bonded firmly to the paper tube without delamination.

[0112] Comparative Example 5

[0113] This comparative example deliberately removes some key process features of the present invention, retaining the basic formula for conventional preparation. Specifically, refer to the raw material ratios and preparation method of Example 1, with the only difference being:

[0114] The drying process uses a single temperature range, drying at 90℃ for 15 minutes, without using segmented gradient drying.

[0115] The obtained base paper was tested according to GB / T2679.8 for ring crush index, GB / T12914 for tensile strength, and UL94 vertical burning method for flame retardancy rating: longitudinal ring crush index 8.5 N·m / g, transverse tensile strength 4.3 kN / m, flame retardancy rating UL94V-1. After 6 months of storage at room temperature, slight powdering and whitening were observed. It was firmly bonded to the white glue of the paper tube without delamination.

[0116] Results Analysis

[0117]

[0118] The ring crush index and tensile strength of the base paper prepared in Examples 1-3 are significantly higher than those of Comparative Examples 1-5. The flame retardant performance of the base paper prepared in Examples 1-3 reaches UL94V-0 level. No flame retardant is released during long-term storage, and it has good compatibility with paper tube adhesive.

[0119] In summary, Comparative Examples 1-5, lacking gradient pulping, fiber crosslinking reinforcement, composite flame retardancy and medium-temperature crosslinking, back-side hydrophobic moisture-proof sizing, and segmented gradient drying processes, exhibited varying degrees of degradation in all performance indicators. Comparative Example 3, lacking both the flame retardant system and crosslinking anchoring, suffered complete loss of flame retardant performance; Comparative Example 2, lacking the crosslinking reinforcing agent, experienced the most severe strength reduction; and Comparative Example 4, lacking the back-side moisture-proof layer, showed significant deterioration in long-term storage stability. This demonstrates that the present invention, through the synergistic effect of gradient pulping, medium-temperature in-situ crosslinking, double-sided differentiated sizing, and segmented drying and curing, effectively solves the problems of easy migration of flame retardants in traditional flame-retardant paper tube base paper, strength attenuation, and difficulty in long-term storage.

[0120] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A halogen-free flame-retardant industrial paper tube base paper, characterized in that: Based on the total mass of oven-dry fibers, the raw material components include the following parts by mass: The composition includes 65-75 parts waste cardboard fiber, 10-15 parts long coniferous fiber, 4-7 parts halogen-free phosphorus-nitrogen-silicon composite flame retardant, 1.2-2.0 parts fiber crosslinking reinforcing agent, 3-5 parts amphoteric starch sizing agent, 0.8-1.5 parts nano silica moisture-proof modifier, and 0.2-0.5 parts polyacrylamide retention aid.

2. The halogen-free flame-retardant industrial paper tube base paper as described in claim 1, characterized in that: The beating degree of the waste cardboard fiber is 38-42°SR.

3. The halogen-free flame-retardant industrial paper tube base paper as described in claim 2, characterized in that: The beating degree of the coniferous long fibers is 45-48°SR.

4. The halogen-free flame-retardant industrial paper tube base paper as described in claim 3, characterized in that: The halogen-free phosphorus-nitrogen-silicon composite flame retardant comprises ammonium polyphosphate, melamine, and nano-organosilicon, mixed in a mass ratio of 5:2:1; the nano-organosilicon is an organosilicon sol with a particle size of 20-50 nm.

5. The halogen-free flame-retardant industrial paper tube base paper as described in claim 4, characterized in that: The fiber crosslinking reinforcing agent includes carboxymethyl cellulose and epoxy crosslinking agent, which are mixed in a mass ratio of 1:1 to 2:

1.

6. The halogen-free flame-retardant industrial paper tube base paper as described in claim 5, characterized in that: The particle size of the nano-silica moisture-proof modifier is 30-60 nm.

7. The halogen-free flame-retardant industrial paper tube base paper as described in claim 1, characterized in that: The base paper includes a paper blank, and a hydrophilic adhesive layer and a hydrophobic flame-retardant and moisture-proof layer are respectively provided on both sides of the paper blank. The hydrophilic adhesive layer is formed by applying an amphoteric starch sizing agent to one side of the paper blank; the hydrophobic flame-retardant and moisture-proof layer is formed by applying an amphoteric starch sizing agent and a nano-silica moisture-proof modifier to the other side of the paper blank.

8. The halogen-free flame-retardant industrial paper tube base paper according to claim 7, characterized in that: The epoxy crosslinking agent is polyamide epichlorohydrin resin.

9. The halogen-free flame-retardant industrial paper tube base paper according to claim 1, characterized in that: The base paper has a longitudinal ring crush index ≥8.5 N·m / g, a transverse tensile strength ≥4.2 kN / m, a vertical flammability rating of UL94V-0, and exhibits no powdering or whitening after 6 months of storage at room temperature, with no degradation in flame retardant performance.

10. A method for preparing the halogen-free flame-retardant industrial paper tube base paper according to any one of claims 1 to 9, characterized in that: Includes the following steps: S1. Fiber pulp compounding: Waste cardboard fiber and softwood long fiber are put into the pulping tank, deionized water is added and stirred evenly to prepare a mixed fiber pulp with a solid content of 3.5-4.5%. S2. In-slurry modification and flame retardant treatment: Add fiber crosslinking reinforcing agent and polyacrylamide retention aid to the mixed fiber slurry in sequence, and stir at 280-320 r / min for 5-8 min; then add halogen-free phosphorus-nitrogen-silicon composite flame retardant, heat to 55-60℃ and stir at a constant temperature for 15-20 min to allow the flame retardant to undergo an in-situ crosslinking reaction with the fiber, and obtain the modified slurry; S3. Papermaking: The modified pulp is dewatered and pressed through the wire section to form a paper blank, and the moisture content of the wet paper is controlled at 40-45%. S4. Double-sided differentiation: A double-sided roller coating process is adopted, with a solution containing amphoteric starch sizing agent coated on the front side of the paper blank and a solution containing amphoteric starch sizing agent and nano-silica moisture-proof modifier coated on the back side of the paper blank. S5. Segmented drying and shaping: A gradient temperature drying process is adopted. The first stage is pre-drying at 70-75℃ for 3-5 minutes, and the second stage is high-temperature curing at 90-95℃ for 8-12 minutes to allow the flame retardant to cross-link and cure in situ. After cooling and humidifying to the moisture content of the finished paper at 6.0-8.0%, it is then calendered and slit to obtain the finished product.

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