A method for preparing a halogen-free flame-retardant phenolic laminated paper board

Abstract

This invention discloses a method for preparing halogen-free flame-retardant phenolic laminated paperboard, including several steps such as paper base flame-retardant treatment, resin synthesis, impregnation and defoaming, pulse hot pressing molding, and post-treatment. By utilizing the synergistic effect of multiple flame retardants, the flame-retardant performance of the laminated paperboard is significantly improved. Defoaming and other treatments are carried out during the use of flame retardants to enhance the bonding between the flame retardants and the resin and laminated paperboard, and to avoid the formation of bubbles during the addition of flame retardants that affect the structural strength of the laminated paperboard. Thus, a halogen-free laminated paperboard with high flame-retardant performance and high strength is obtained, meeting higher environmental protection requirements.

Description

Technical Field

[0001] This invention belongs to the field of laminate technology, specifically relating to a method for preparing halogen-free flame-retardant phenolic laminate paperboard. Background Technology

[0002] Laminates are a type of laminated product. Laminates are made by laminating and hot-pressing two or more layers of resin-impregnated fibers or fabrics together. Laminates can be processed into various insulating and structural components and are widely used in motors, transformers, high and low voltage electrical appliances, electrical instruments, and electronic equipment. Depending on the application environment, different performance parameters of the laminates are required.

[0003] Flame retardancy is a crucial safety parameter for laminates, especially when they are used in various electrical appliances, building decorations, furniture manufacturing, and insulation materials. Laminates with good flame retardancy can effectively control the spread of fire, ensure safety, and reduce losses. Current technologies typically improve the flame retardancy of laminates by adding flame retardants during the laminate manufacturing process. Furthermore, to meet environmental protection requirements, halogen-free flame retardants such as alkyl hypophosphites are usually chosen. While introducing flame retardants can give laminates a certain degree of flame retardancy, they still exhibit high smoke density and heat release rate peaks during testing, posing a significant threat to personal safety and property in the event of a fire. Additionally, the introduction of flame retardants can lead to poor bonding between the laminate matrix and the phenolic resin, severely affecting the strength and performance of the laminate. Summary of the Invention

[0004] This invention provides a method for preparing halogen-free flame-retardant phenolic laminated paperboard to solve at least one of the above-mentioned technical problems.

[0005] The technical solution adopted in this invention is: a method for preparing halogen-free flame-retardant phenolic laminated paperboard, comprising the following steps:

[0006] S1: Paper-based flame retardant treatment: The paper base is impregnated in an aqueous emulsion containing 10wt%-15wt% ammonium polyphosphate and 5wt%-8wt% zinc borate. The paper base can be cotton linter paper. Vacuum-assisted impregnation is used during impregnation, and the vacuum degree is set to 0.06-0.09MPa. After drying, a flame retardant paper base with a flame retardant loading of 18wt%-25wt% is obtained.

[0007] S2: Resin synthesis: Phenol, formaldehyde and DOPO are reacted under alkaline conditions in a molar ratio of 1:1.8-2.2:0.2-0.4 to obtain a flame-retardant resin with a phosphorus content ≥3wt%;

[0008] S3: Impregnation and defoaming: After stacking the flame-retardant paper base layer, impregnate it in flame-retardant resin, place an ultrasonic vibrator in the impregnation tank and apply ultrasonic waves with a frequency of 28-32kHz and a power density of 100-150W / m², impregnate for 2-4 minutes, repeat 3-4 times to obtain the laminate blank.

[0009] S4: Pulse hot pressing molding:

[0010] Initial stage: The laminate blank is subjected to a pulse hot press at a temperature of 125-135℃, a pressure of 4-6MPa, and a pulse frequency of 2-4 times / min for 15-20 minutes.

[0011] Main curing stage: heat to 155-165℃, pressure 10-15MPa, hold pressure for 40-50 minutes to obtain laminate semi-finished product;

[0012] S5: Post-treatment: Roller-coating a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite onto the surface of the semi-finished laminate. After roller coating, cure at 100-110℃ for 2-3 hours to obtain halogen-free flame-retardant laminated paperboard.

[0013] In a preferred embodiment, in step S1, 0.5wt%-1.5wt% of polyether-modified siloxane defoamer is added to the aqueous emulsion. The amount of defoamer is based on the weight of the aqueous emulsion, and the paper base weight is 120-180 g / m².

[0014] In a preferred embodiment, in step S1, the paper base is aramid fiber reinforced paper with an aramid content of 15wt%-25wt%, and the fiber is surface modified with phosphate ester.

[0015] In a preferred embodiment, in step S2, 1wt%-2wt% of anatase nano-titanium dioxide with a particle size between 20-50nm is added to the flame retardant resin, the amount of nano-titanium dioxide being based on the weight of the flame retardant resin, so that the char residue rate of the flame retardant resin is ≥30%.

[0016] In a preferred embodiment, in step S3, 3wt%-8wt% of a microencapsulated flame retardant with a particle size of 5-20μm is added to the flame retardant resin during impregnation. The amount of the microencapsulated flame retardant added is based on the weight of the flame retardant resin. The capsule wall of the microencapsulated flame retardant is melamine resin, and the core material is ammonium polyphosphate.

[0017] In a preferred embodiment, in step S3, microwave drying is performed after each impregnation, with a microwave power of 600-800W and a time of 40-60s, so that the volatile content is ≤2.5%.

[0018] In a preferred embodiment, in step S3, after ultrasonic treatment, the paper substrate is subjected to infrared thermal imaging detection to eliminate local temperature abnormalities with a temperature difference > 5°C.

[0019] In a preferred embodiment, in step S4, nitrogen gas with a flow rate of 5-10 L / min is introduced during pulse hot pressing to suppress the generation of oxidation bubbles.

[0020] In a preferred embodiment, in step S5, the flame-retardant coating further comprises 0.5wt%-1wt% carbon nanotubes, the carbon nanotubes having a diameter of 10-30 nm, an aspect ratio > 100, and a coating resistivity ≤ 10. 6 Ω·cm.

[0021] The halogen-free flame-retardant phenolic laminate paperboard prepared by the aforementioned method has the following characteristics:

[0022] (a) Smoke density rating (SDR) ≤ 50;

[0023] (b) Peak heat release rate ≤ 120 kW / m²;

[0024] (c) Interfacial bonding strength ≥ 2.5 MPa;

[0025] (d) Contains 3wt%-8wt% of microencapsulated flame retardant with a particle size of 5-20μm, wherein the capsule wall of the microencapsulated flame retardant is melamine resin and the core material is ammonium polyphosphate.

[0026] Due to the adoption of the above technical solution, the beneficial effects achieved by this invention are as follows:

[0027] 1. As a preferred embodiment of the present invention, by utilizing the synergistic effect of ammonium polyphosphate and zinc borate flame retardant, with ammonium polyphosphate acting as an acid source and carbonizing agent and zinc borate acting as a synergist, the amount of ammonium polyphosphate added can be reduced while inhibiting smoke generation.

[0028] 2. In a preferred embodiment of the present invention, DOPO is chemically bonded to the resin molecular chain to provide durable flame retardancy; ammonium polyphosphate and zinc borate flame retardants, as physically added flame retardants, supplement the flame retardant effects of the gas phase and condensed phase, avoid the migration problem when DOPO is used alone, and reduce the total amount of flame retardant added.

[0029] 3. As a preferred embodiment of the present invention, the microencapsulated flame retardant can improve the thermal stability of the flame retardant and avoid premature decomposition during processing; the nano-montmorillonite forms a physical barrier through the intercalation structure, enhancing the coating's impermeability and high-temperature resistance.

[0030] 4. As a preferred embodiment of the present invention, by utilizing measures such as impregnation defoaming, pulse hot pressing molding, microwave drying, and nitrogen defoaming, the total amount of flame retardant added is controlled, the compatibility between each flame retardant and the resin is improved, and the synergistic efficiency of each flame retardant is enhanced. Detailed Implementation

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0032] Example 1

[0033] The preparation of halogen-free flame-retardant laminated paperboard includes the following steps:

[0034] S1: Paper-based flame retardant treatment: The paper base is impregnated in an aqueous emulsion containing 12wt%-15wt% ammonium polyphosphate and 7wt%-8wt% zinc borate. The paper base is selected as cotton lint paper. Vacuum-assisted impregnation is used during impregnation, and the vacuum degree is set to 0.07-0.09MPa. After drying, a flame retardant paper base with a flame retardant loading of 22wt%-25wt% is obtained.

[0035] S2: Resin synthesis: Phenol, formaldehyde and DOPO are reacted under alkaline conditions in a molar ratio of 1:2.0-2.2:0.3-0.4 to obtain a flame-retardant resin with a phosphorus content ≥3wt%;

[0036] S3: Impregnation and defoaming: After stacking the flame-retardant paper base layer, impregnate it in flame-retardant resin, place an ultrasonic vibrator in the impregnation tank and apply ultrasonic waves with a frequency of 28-30kHz and a power density of 100-120W / m², impregnate for 3-4 minutes, repeat 3-4 times to obtain the laminate blank.

[0037] S4: Pulse hot pressing molding:

[0038] Initial stage: The laminate blank is subjected to a pulse hot press at a temperature of 125-130℃, a pressure of 5-6MPa, and a pulse frequency of 3-4 times / min for 15-20 minutes.

[0039] Main curing stage: heat to 155-160℃, pressure 12-15MPa, hold pressure for 40-50 minutes to obtain laminate semi-finished product;

[0040] S5: Post-treatment: Roller-coating a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite onto the surface of the semi-finished laminate. After roller coating, cure at 100-110℃ for 2-3 hours to obtain halogen-free flame-retardant laminated paperboard.

[0041] Example 2

[0042] The preparation of halogen-free flame-retardant laminated paperboard includes the following steps:

[0043] S1: Paper base flame retardant treatment: The paper base is impregnated in an aqueous emulsion containing 10wt%-12wt% ammonium polyphosphate and 5wt%-6wt% zinc borate. The paper base is aramid fiber reinforced paper with an aramid content of 15wt%-25wt%, and the fiber is modified with phosphate ester surface. Vacuum-assisted impregnation is used during impregnation, and the vacuum degree is set to 0.06-0.08MPa. After drying, a flame retardant paper base with a flame retardant loading of 18wt%-20wt% is obtained.

[0044] S2: Resin synthesis: Phenol, formaldehyde and DOPO are reacted under alkaline conditions in a molar ratio of 1:1.8-2.0:0.2-0.3 to obtain a flame-retardant resin with a phosphorus content ≥3wt%;

[0045] S3: Impregnation and defoaming: After stacking the flame-retardant paper base layer, impregnate it in flame-retardant resin, place an ultrasonic vibrator in the impregnation tank and apply ultrasonic waves with a frequency of 30-32kHz and a power density of 130-150W / m², impregnate for 2-3 minutes, repeat 3-4 times to obtain the laminate blank.

[0046] S4: Pulse hot pressing molding:

[0047] Initial stage: The laminate blank is subjected to a pulse hot press at a temperature of 130-135℃, a pressure of 4-5MPa, and a pulse frequency of 2-3 times / min for 15-20 minutes.

[0048] Main curing stage: heat to 160-165℃, pressure 10-12MPa, hold pressure for 40-50 minutes to obtain laminate semi-finished product;

[0049] S5: Post-treatment: Roller-coating a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite onto the surface of the semi-finished laminate. After roller coating, cure at 100-110℃ for 2-3 hours to obtain halogen-free flame-retardant laminated paperboard.

[0050] Example 3

[0051] The preparation of halogen-free flame-retardant laminated paperboard includes the following steps:

[0052] S1: Flame-retardant treatment of paper base: The paper base is impregnated in an aqueous emulsion containing 12wt%-13wt% ammonium polyphosphate and 6wt%-7wt% zinc borate. 0.5wt%-1.5wt% polyether-modified siloxane defoamer is added to the aqueous emulsion, the amount of defoamer being based on the weight of the aqueous emulsion. The paper base is selected as lint paper with a basis weight of 120-180 g / m². Vacuum-assisted impregnation is used, with a vacuum degree set at 0.08-0.09 MPa. After drying, a flame-retardant paper base with a flame retardant loading of 20wt%-22wt% is obtained.

[0053] S2: Resin synthesis: Phenol, formaldehyde and DOPO are reacted under alkaline conditions in a molar ratio of 1:1.9-2.1:0.3-0.4 to obtain a flame-retardant resin with a phosphorus content ≥3wt%;

[0054] S3: Impregnation and defoaming: After stacking the flame-retardant paper base layer, impregnate it in flame-retardant resin, place an ultrasonic vibrator in the impregnation tank and apply ultrasonic waves with a frequency of 29-30kHz and a power density of 120-130W / m², impregnate for 3-4 minutes, repeat 3-4 times to obtain the laminate blank.

[0055] S4: Pulse hot pressing molding:

[0056] Initial stage: The laminate blank is subjected to a pulse hot press at a temperature of 125-130℃, a pressure of 4-5MPa, and a pulse frequency of 3-4 times / min for 15-20 minutes.

[0057] Main curing stage: heat to 155-160℃, pressure 11-12MPa, hold pressure for 40-50 minutes to obtain laminate semi-finished product;

[0058] S5: Post-treatment: Roller-coating a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite onto the surface of the semi-finished laminate. After roller coating, cure at 100-110℃ for 2-3 hours to obtain halogen-free flame-retardant laminated paperboard.

[0059] Example 4

[0060] Same as Example 3, halogen-free flame-retardant laminated paperboard was prepared, the difference being:

[0061] In step S2, 1wt%-2wt% of anatase nano-titanium dioxide with a particle size between 20-50nm is added to the flame retardant resin. The amount of nano-titanium dioxide is based on the weight of the flame retardant resin, so that the char residue of the flame retardant resin is ≥30%.

[0062] Example 5

[0063] Same as Example 4, halogen-free flame-retardant laminated paperboard was prepared, the difference being:

[0064] In step S3, 3wt%-8wt% of microencapsulated flame retardant with a particle size of 5-20μm is added to the flame retardant resin during impregnation. The amount of microencapsulated flame retardant added is based on the weight of the flame retardant resin. The capsule wall of the microencapsulated flame retardant is melamine resin, and the core material is ammonium polyphosphate.

[0065] Example 6

[0066] Same as Example 5, halogen-free flame-retardant laminated paperboard was prepared, the difference being:

[0067] In step S3, microwave drying is performed after each impregnation. The microwave power is 600-800W and the time is 40-60s, so that the volatile content is ≤2.5%.

[0068] Example 7

[0069] Same as Example 6, halogen-free flame-retardant laminated paperboard was prepared, the difference being:

[0070] In step S3, after ultrasonic treatment, infrared thermal imaging is performed on the paper substrate to eliminate local temperature abnormalities with a temperature difference greater than 5°C.

[0071] Example 8

[0072] Same as Example 7, halogen-free flame-retardant laminated paperboard was prepared, the difference being:

[0073] In step S4, nitrogen gas with a flow rate of 5-10 L / min is introduced during pulse hot pressing to suppress the generation of oxidation bubbles.

[0074] Example 9

[0075] Same as Example 8, halogen-free flame-retardant laminated paperboard was prepared, the difference being:

[0076] In step S5, the flame-retardant coating further comprises 0.5wt%-1wt% carbon nanotubes, the carbon nanotubes having a diameter of 10-30nm, an aspect ratio >100, and a coating resistivity ≤10. 6 Ω·cm.

[0077] Comparative Example 1

[0078] Similar to Example 1, in the preparation of halogen-free flame-retardant laminated paperboard, the flame-retardant treatment of the paper base in step S1 is carried out normally, and subsequent steps are performed normally.

[0079] Comparative Example 2

[0080] Similar to Example 1, in the preparation of halogen-free flame-retardant laminated paperboard, DOPO is not added during the resin synthesis process in step S2.

[0081] Comparative Example 3

[0082] Similar to Example 1, the ultrasonic impregnation and defoaming process in step S3 is not performed when preparing halogen-free flame-retardant laminated paperboard.

[0083] Comparative Example 4

[0084] Similar to Example 1, in preparing halogen-free flame-retardant laminated paperboard, step S4 uses the traditional hot pressing method and does not perform pulse hot pressing.

[0085] Comparative Example 5

[0086] Similar to Example 1, the post-processing operation in step S5 is not performed when preparing halogen-free flame-retardant laminated paperboard.

[0087] Table 1 shows the test results of smoke density rating (SDR), peak heat release rate, and interfacial bonding strength for Examples 1-9 and Comparative Examples 1-4.

[0088] The smoke density rating is determined using a smoke density tester (such as the JCY-3 touchscreen smoke density tester) according to the standard methods of GB / T8627-2007 or GB 8624-2012; the peak heat release rate is determined using a cone calorimeter according to the standard methods of ISO 5660-1:2015 or GB / T 16172-2007; and the interfacial bonding strength is determined using tensile or shear tests according to the standard methods of GB / T 7124-2008 or with reference to JC / T 2850-2024.

[0089] Each test result is the average of 10 test results obtained from the same batch of samples in the same embodiment or comparative example, after removing the maximum and minimum values.

[0090] Table 1 shows the test results of smoke density level, peak heat release rate, and interfacial bonding strength for Examples 1-9 and Comparative Examples 1-4.

[0091]

[0092] Table 1, comparing the data from Example 1 and Comparative Examples 1-5, shows that the flame-retardant treatment of the paper base, the flame-retardant resin, and the post-treatment have a synergistic effect, significantly reducing the smoke density rating and peak heat release rate. Impregnation defoaming and pulse hot pressing play an auxiliary role in the synergistic effect of the flame retardants, not only reducing the smoke density rating and peak heat release rate but also improving the bonding between the flame retardant and the laminate, thus increasing the interfacial bonding strength. Comparing the data from Example 1 and Example 2, it is clear that the material of the paper base affects the smoke density rating, peak heat release rate, and interfacial bonding strength, with the effect stemming from the flame retardant loading. Comparing Example 1 and Example 3, it can be seen that the introduction of defoamer enhances the synergistic effect of the flame retardants, significantly reducing the smoke density rating and peak heat release rate, while also improving the interfacial bonding strength due to the reduction of bubbles. Comparative data from Examples 3-9 show that the introduction of nano-titanium dioxide and microencapsulated flame retardants, through the synergistic effect of impregnation defoaming and pulse hot pressing, improves the compatibility between the defoamer and the resin, ultimately resulting in a reduction in smoke density and peak heat release rate, while also slightly improving interfacial bonding strength. Microwave drying, removal, and nitrogen defoaming further enhance the synergistic effect of the various flame retardants. Finally, the introduction of a carbon nanotube coating in the post-treatment further improves the overall effect.

[0093] For any parts not mentioned in this invention, existing technologies can be used or referenced.

[0094] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0095] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing halogen-free flame-retardant phenolic laminated paperboard, characterized in that, Includes the following steps: S1: Flame retardant treatment of paper base: The paper base is impregnated in an aqueous emulsion containing 10wt%-15wt% ammonium polyphosphate and 5wt%-8wt% zinc borate. The paper base is aramid fiber reinforced paper with an aramid content of 15wt%-25wt%, and the fibers are modified with phosphate ester surface. 0.5wt%-1.5wt% polyether modified siloxane defoamer is added to the aqueous emulsion, and the paper base basis weight is 120-180g / m². Vacuum-assisted impregnation is carried out under a vacuum degree of 0.06-0.09MPa. After drying, a flame retardant paper base with a flame retardant loading of 18wt%-25wt% is obtained. S2: Resin Synthesis: Phenol, formaldehyde, and DOPO are reacted under alkaline conditions in a molar ratio of 1:1.8-2.2:0.2-0.4 to obtain a flame-retardant resin with a phosphorus content ≥3wt%. 1wt%-2wt% of anatase nano-titanium dioxide with a particle size between 20-50nm is added to the resin to make the char residue of the flame-retardant resin ≥30%. S3: Impregnation and defoaming: The flame-retardant paper base layer is stacked and impregnated in flame-retardant resin. Ultrasonic waves with a frequency of 28-32kHz and a power density of 100-150W / m² are applied in the impregnation tank for 2-4 minutes. The impregnation is repeated 3-4 times to obtain a laminate blank. During impregnation, 3wt%-8wt% of microencapsulated flame retardant with a particle size of 5-20μm is added to the flame-retardant resin. The capsule wall of the microencapsulated flame retardant is melamine resin and the core material is ammonium polyphosphate. S4: Pulse hot pressing molding: Initial stage: The laminate blank is kept at a temperature of 125-135℃, a pressure of 4-6MPa, and a pulse frequency of 2-4 times / min for 15-20 minutes. Main curing stage: heat to 155-165℃, pressure 10-15MPa, hold pressure for 40-50 minutes to obtain laminate semi-finished product; S5: Post-treatment: Roll-coat the surface of the semi-finished laminate with a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite, and cure at 100-110℃ for 2-3 hours to obtain halogen-free flame-retardant laminated paperboard.

2. The method for preparing halogen-free flame-retardant phenolic laminated paperboard according to claim 1, characterized in that, In step S3, microwave drying is performed after each impregnation. The microwave power is 600-800W and the time is 40-60s, so that the volatile content is ≤2.5%.

3. The method for preparing halogen-free flame-retardant phenolic laminated paperboard according to claim 1, characterized in that, In step S3, after ultrasonic treatment, infrared thermal imaging is performed on the paper substrate to eliminate local temperature abnormalities with a temperature difference greater than 5°C.

4. The method for preparing halogen-free flame-retardant phenolic laminated paperboard according to claim 1, characterized in that, In step S4, nitrogen gas with a flow rate of 5-10 L / min is introduced during pulse hot pressing to suppress the generation of oxidation bubbles.

5. The method for preparing halogen-free flame-retardant phenolic laminated paperboard according to claim 1, characterized in that, In step S5, the flame-retardant coating further comprises 0.5wt%-1wt% carbon nanotubes, the carbon nanotubes having a diameter of 10-30nm, an aspect ratio >100, and a coating resistivity ≤10. 6 Ω·cm.

6. A halogen-free flame-retardant phenolic laminated paperboard, prepared by the method according to any one of claims 1-5, characterized in that: (a) Smoke density rating (SDR) ≤ 50; (b) Peak heat release rate ≤ 120 kW / m²; (c) Interfacial bonding strength ≥ 2.5 MPa.

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