Preparation method of halogen-free flame-retardant phenolic aldehyde laminated paperboard

Abstract

The invention discloses a preparation method of a halogen-free flame-retardant phenolic aldehyde laminated paperboard, which comprises the steps of paper-based flame-retardant treatment, resin synthesis, dipping defoaming, pulse hot-press molding, post-treatment and the like, the flame-retardant property of the laminated paperboard is obviously improved by utilizing the synergistic effect of various flame retardants, and the treatment such as defoaming is performed in the process of utilizing the flame retardants, so that the flame-retardant property of the laminated paperboard is improved. The flame retardant is added into the resin, so that the bonding property of the flame retardant with the resin and the laminated paperboard is enhanced, and the influence on the structural strength of the laminated paperboard caused by bubbles generated in the flame retardant adding process is avoided, so that the halogen-free laminated paperboard with high flame retardant property and high strength is obtained, and the higher-grade environment-friendly requirement is met.

Description

Technical Field

[0001] The invention belongs to the technical field of laminated boards, and particularly relates to a preparation method of a halogen-free flame-retardant phenolic laminated paperboard. Background Art

[0002] Laminate is a type of laminated product. Laminates are made by laminating and heat-pressing two or more layers of resin-impregnated fibers or fabrics. Laminates can be processed into various insulating and structural components and are widely used in motors, transformers, high- and low-voltage electrical equipment, electrical instruments, and electronic equipment. The performance requirements for laminates vary depending on the environment in which they are used.

[0003] Flame retardant performance is one of the important safety parameters of laminates, especially when laminates are used in various electrical equipment, building decoration, furniture manufacturing and insulation materials. Laminates with good flame retardant performance can effectively control the spread of fire, ensure safety and reduce losses. In the prior art, in order to improve the flame retardant performance of laminates, flame retardants are usually added during the preparation of laminates. Furthermore, when adding flame retardants, halogen-free flame retardants such as alkyl hypophosphites are usually selected to meet the requirements of environmental protection levels. After the introduction of flame retardants, although the laminates can obtain a certain degree of flame retardant performance, they still have the defects of high smoke density level and heat release rate peak value during the test process. In the event of a fire, it poses a great threat to personal and property safety. At the same time, after the introduction of flame retardants, the laminate matrix and phenolic resin are prone to poor bonding problems, which seriously affect the strength and performance of the laminates. Summary of the Invention

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

[0005] The technical solution adopted by the present invention is: a method for preparing a halogen-free flame-retardant phenolic laminated paperboard, comprising the following steps: S1: flame retardant treatment of paper base: impregnating the paper base in an aqueous emulsion containing 10wt%-15wt% ammonium polyphosphate and 5wt%-8wt% zinc borate, wherein the paper base can be selected from cotton linter paper, and vacuum assisted impregnation is used during the 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; S2: Resin synthesis: Phenol, formaldehyde, and DOPO are reacted in a molar ratio of 1:1.8-2.2:0.2-0.4 under alkaline conditions to obtain a flame retardant resin with a phosphorus content of ≥3 wt%; S3: Impregnation and defoaming: After stacking the flame retardant paper base, impregnate it in the flame retardant resin, and 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. The impregnation time is 2-4 minutes, and this process is repeated 3-4 times to obtain a rough laminate. S4: Pulse hot pressing: Initial stage: Use pulse hot press to heat the laminated board blank 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: heating to 155-165℃, pressure 10-15MPa, maintaining pressure for 40-50 minutes to obtain semi-finished laminated board; S5: Post-treatment: Roll-coat a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite on the surface of the semi-finished laminated board. After roller coating, cure the coating at 100-110°C for 2-3 hours to obtain a halogen-free flame-retardant laminated paperboard.

[0006] In a preferred embodiment, in step S1, 0.5 wt%-1.5 wt% of a polyether-modified silicone defoamer is added to the aqueous emulsion, the amount of the defoamer is calculated based on the weight of the aqueous emulsion, and the paper base weight is 120-180 g / m².

[0007] 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.

[0008] In a preferred embodiment, in step S2, 1wt%-2wt% of anatase-type nano-titanium dioxide with a particle size between 20-50nm is added to the flame retardant resin, and the amount of nano-titanium dioxide is such that the residual carbon rate of the flame retardant resin is ≥30% based on the weight of the flame retardant resin.

[0009] In a preferred embodiment, in step S3, 3wt%-8wt% of a microencapsulated flame retardant with a particle size of 5-20 μm is added to the flame retardant resin during impregnation, and 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.

[0010] In a preferred embodiment, in step S3, microwave drying is performed after each immersion, with a microwave power of 600-800 W and a drying time of 40-60 s to reduce the volatile matter content to ≤2.5%.

[0011] In a preferred embodiment, in step S3, infrared thermal imaging is performed on the paper base after the ultrasonic wave is applied, and local temperature abnormal areas with a temperature difference greater than 5° C. are eliminated.

[0012] In a preferred embodiment, in step S4, nitrogen gas is introduced at a flow rate of 5-10 L / min during the pulse hot pressing to suppress the generation of oxidation bubbles.

[0013] In a preferred embodiment, in step S5, the flame retardant coating further comprises 0.5wt%-1wt% carbon nanotubes, the diameter of the carbon nanotubes is 10-30nm, the aspect ratio is greater than 100, and the coating resistivity is ≤10 6 Ω·cm.

[0014] The halogen-free flame-retardant phenolic laminated paperboard prepared by the above method has the following characteristics: (a) Smoke density rating (SDR) ≤ 50; (b) Peak heat release rate ≤ 120 kW / m²; (c) Interface bonding strength ≥ 2.5 MPa; (d) Containing 3wt%-8wt% of a microencapsulated flame retardant with a particle size of 5-20 μm, the capsule wall of the microencapsulated flame retardant is melamine resin, and the core material is ammonium polyphosphate.

[0015] Due to the adoption of the above technical solution, the beneficial effects achieved by the present invention are as follows: 1. As a preferred embodiment of the present invention, by utilizing the synergistic effect of ammonium polyphosphate and zinc borate flame retardant, ammonium polyphosphate serves as an acid source and carbonizing agent, and zinc borate serves as a synergist, the amount of ammonium polyphosphate added can be reduced while suppressing smoke generation.

[0016] 2. As a preferred embodiment of the present invention, DOPO provides durable flame retardancy by chemically bonding to the resin molecular chain; ammonium polyphosphate and zinc borate flame retardants serve as physically added flame retardants to supplement the gas phase and condensed phase flame retardant effects, avoiding the migration problem when DOPO is used alone, while reducing the total amount of flame retardant added.

[0017] 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 anti-permeability and high temperature resistance of the coating.

[0018] 4. As a preferred embodiment of the present invention, by utilizing immersion defoaming and pulse hot pressing molding as well as microwave drying and nitrogen defoaming measures, the total amount of flame retardant added is controlled, the compatibility of each flame retardant with the resin is improved, which is beneficial to the synergistic efficiency of each flame retardant. DETAILED DESCRIPTION

[0019] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0020] Example 1 Preparation of halogen-free flame-retardant laminated paperboard, comprising the following steps: S1: flame retardant treatment of paper base: impregnating the paper base in an aqueous emulsion containing 12wt%-15wt% ammonium polyphosphate and 7wt%-8wt% zinc borate, wherein cotton linter paper is selected as the paper base, and vacuum assisted impregnation is adopted during the 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; S2: Resin synthesis: Phenol, formaldehyde, and DOPO are reacted in a molar ratio of 1:2.0-2.2:0.3-0.4 under alkaline conditions to obtain a flame retardant resin having a phosphorus content ≥3 wt%; S3: Impregnation and defoaming: After stacking the flame retardant paper base, impregnate it in the flame retardant resin, and 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. The impregnation time is 3-4 minutes, and this process is repeated 3-4 times to obtain a rough laminate. S4: Pulse hot pressing: Initial stage: Use pulse hot press to heat the laminated board blank at a temperature of 125-130℃, a pressure of 5-6MPa, and a pulse frequency of 3-4 times / min for 15-20 minutes; Main curing stage: heating to 155-160℃, pressure 12-15MPa, maintaining pressure for 40-50 minutes to obtain semi-finished laminated board; S5: Post-treatment: Roll-coat a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite on the surface of the semi-finished laminated board. After roller coating, cure the coating at 100-110°C for 2-3 hours to obtain a halogen-free flame-retardant laminated paperboard.

[0021] Example 2 Preparation of halogen-free flame-retardant laminated paperboard, comprising the following steps: S1: flame retardant treatment of paper base: impregnating the paper base in an aqueous emulsion containing 10wt%-12wt% ammonium polyphosphate and 5wt%-6wt% zinc borate, wherein the paper base is aramid fiber reinforced paper with an aramid content of 15wt%-25wt%, and the fiber is surface-modified with phosphate ester, and vacuum-assisted impregnation is used during the 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; S2: Resin synthesis: Phenol, formaldehyde and DOPO are reacted in a molar ratio of 1:1.8-2.0:0.2-0.3 under alkaline conditions to obtain a flame retardant resin with a phosphorus content of ≥3 wt%; S3: Impregnation and defoaming: After stacking the flame retardant paper base, impregnate it in the flame retardant resin, and 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. The impregnation time is 2-3 minutes, and this process is repeated 3-4 times to obtain a rough laminate. S4: Pulse hot pressing: Initial stage: Use pulse hot press to heat the laminated board blank at a temperature of 130-135℃, a pressure of 4-5MPa, and a pulse frequency of 2-3 times / min for 15-20 minutes; Main curing stage: heating to 160-165℃, pressure 10-12MPa, maintaining pressure for 40-50 minutes to obtain semi-finished laminated board; S5: Post-treatment: Roll-coat a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite on the surface of the semi-finished laminated board. After roller coating, cure the coating at 100-110°C for 2-3 hours to obtain a halogen-free flame-retardant laminated paperboard.

[0022] Example 3 Preparation of halogen-free flame-retardant laminated paperboard, comprising the following steps: S1: Flame retardant treatment of paper: 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, with the amount of defoamer being based on the weight of the aqueous emulsion. Cotton linter paper is selected as the paper base, and the paper base weight is 120-180g / m². Vacuum assisted impregnation is used during impregnation, and the vacuum level is set at 0.08-0.09MPa. After drying, a flame retardant loading of 20wt%-22wt% is obtained. S2: Resin synthesis: Phenol, formaldehyde, and DOPO are reacted in a molar ratio of 1:1.9-2.1:0.3-0.4 under alkaline conditions to obtain a flame retardant resin having a phosphorus content ≥3 wt%; S3: Impregnation and defoaming: After stacking the flame retardant paper base, impregnate it in the flame retardant resin, and 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. The impregnation time is 3-4 minutes, and this process is repeated 3-4 times to obtain a rough laminate. S4: Pulse hot pressing: Initial stage: Use pulse hot press to heat the laminated board blank at a temperature of 125-130℃, a pressure of 4-5MPa, and a pulse frequency of 3-4 times / min for 15-20 minutes; Main curing stage: heating to 155-160℃, pressure 11-12MPa, maintaining pressure for 40-50 minutes to obtain semi-finished laminated board; S5: Post-treatment: Roll-coat a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite on the surface of the semi-finished laminated board. After roller coating, cure the coating at 100-110°C for 2-3 hours to obtain a halogen-free flame-retardant laminated paperboard.

[0023] Example 4 The same method as in Example 3 was used to prepare a halogen-free flame-retardant laminated paperboard, except that: In step S2, 1 wt% to 2 wt% of anatase nano-titanium dioxide with a particle size of 20-50 nm is added to the flame retardant resin. The amount of the nano-titanium dioxide is such that the residual carbon rate of the flame retardant resin is ≥30% based on the weight of the flame retardant resin.

[0024] Example 5 The same method as in Example 4 was used to prepare a halogen-free flame-retardant laminated paperboard, except that: In step S3, 3wt%-8wt% of a microencapsulated flame retardant with a particle size of 5-20 μm 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.

[0025] Example 6 The same method as in Example 5 was used to prepare a halogen-free flame-retardant laminated paperboard, except that: In step S3, microwave drying is performed after each immersion, with a microwave power of 600-800 W and a drying time of 40-60 s to make the volatile matter content ≤2.5%.

[0026] Example 7 The same method as Example 6 was used to prepare a halogen-free flame-retardant laminated paperboard, except that: In step S3, after the ultrasonic wave is applied, infrared thermal imaging is performed on the paper substrate to remove abnormal local temperature areas with a temperature difference greater than 5°C.

[0027] Example 8 The same method as in Example 7 was used to prepare a halogen-free flame-retardant laminated paperboard, except that: In step S4, nitrogen gas is introduced at a flow rate of 5-10 L / min during the pulse hot pressing to suppress the generation of oxidation bubbles.

[0028] Example 9 The same method as in Example 8 was used to prepare a halogen-free flame-retardant laminated paperboard, except that: In step S5, the flame retardant coating further comprises 0.5wt%-1wt% carbon nanotubes, the diameter of the carbon nanotubes is 10-30nm, the aspect ratio is greater than 100, and the coating resistivity is ≤10 6 Ω·cm.

[0029] Comparative Example 1 As in Example 1, when preparing the halogen-free flame-retardant laminated paperboard, the paper base is flame-retarded in step S1, and the subsequent steps are carried out normally.

[0030] Comparative Example 2 Similar to Example 1, when preparing the halogen-free flame-retardant laminated paperboard, no DOPO is added during the resin synthesis in step S2.

[0031] Comparative Example 3 Similar to Example 1, when preparing the halogen-free flame-retardant laminated paperboard, the ultrasonic impregnation defoaming process in step S3 is not performed.

[0032] Comparative Example 4 Similar to Example 1, when preparing the halogen-free flame-retardant laminated paperboard, step S4 adopts the traditional hot pressing method without pulse hot pressing operation.

[0033] Comparative Example 5 Similar to Example 1, when preparing the halogen-free flame-retardant laminated paperboard, the post-processing operation process of step S5 is not performed.

[0034] Table 1 shows the test results of smoke density rating (SDR), peak heat release rate, and interface bonding strength of Examples 1-9 and Comparative Examples 1-4.

[0035] The smoke density level is measured using a smoke density tester (such as the JCY-3 touch screen smoke density tester) in accordance with the standard methods of GB / T8627-2007 or GB 8624-2012. The peak heat release rate is measured using a cone calorimeter in accordance with the standard methods of ISO 5660-1:2015 or GB / T 16172-2007. The interface bonding strength is measured using a tensile or shear test in accordance with the standard methods of GB / T 7124-2008 or JC / T 2850-2024.

[0036] Each test result is the average value of 10 experimental results of the same batch of samples obtained in the same embodiment or comparative example after removing the maximum and minimum values.

[0037] Table 1 Test results of smoke density level, peak heat release rate and interface bonding strength of Examples 1-9 and Comparative Examples 1-4

[0038] By the data of Table 1, Comparative Example 1 and Comparative Examples 1-5, it can be seen that the flame retardant treatment, flame retardant resin and post-treatment of the paper base have a synergistic effect, which can significantly reduce the smoke density level and the peak heat release rate. Impregnation defoaming and pulse hot pressing molding have played an auxiliary role in the synergy of each flame retardant, which can not only reduce the smoke density level and the peak heat release rate, but also improve the combination of the flame retardant and the laminate, and improve the interface bonding strength. Comparative Example 1 and Example 2 data show that the material of the paper base will have an impact on the smoke density level, the peak heat release rate and the interface bonding strength, and its impact comes from the loading amount of the flame retardant. Comparative Example 1 and Example 3 can be seen that the introduction of the defoamer enhances the synergistic effect of each flame retardant, significantly reducing the smoke density level and the peak heat release rate, while improving the interface bonding strength due to the reduction of bubbles. By comparing the data of Examples 3-9, it can be seen that after the introduction of nano-titanium dioxide and microencapsulated flame retardants, the compatibility of the defoamer with the resin can also be improved under the synergistic effect of impregnation defoaming and pulse hot pressing, which is ultimately reflected in the reduction of smoke density level and peak heat release rate, and on this basis, the interfacial bonding strength is still slightly improved. After adopting microwave drying, removal and nitrogen defoaming, the synergy of each flame retardant can be further improved. Finally, in post-processing, the introduction of carbon nanotube coating can further enhance its effect.

[0039] Anything not described in the present invention can be achieved by adopting or drawing on existing technologies.

[0040] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0041] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a halogen-free flame-retardant phenolic laminated paperboard, characterized in that: The following steps are involved: S1: flame retardant treatment of paper base: impregnating the paper base in an aqueous emulsion containing 10wt%-15wt% ammonium polyphosphate and 5wt%-8wt% zinc borate, vacuum-assisted impregnation under a vacuum degree of 0.06-0.09MPa, and drying to obtain a flame retardant paper base with a flame retardant loading of 18wt%-25wt%; S2: Resin synthesis: Phenol, formaldehyde, and DOPO are reacted in a molar ratio of 1:1.8-2.2:0.2-0.4 under alkaline conditions to obtain a flame retardant resin with a phosphorus content of ≥3 wt%; S3: Impregnation and defoaming: After stacking the flame retardant paper base, impregnate it in the flame retardant resin, and apply ultrasonic waves with a frequency of 28-32kHz and a power density of 100-150W / m² in the impregnation tank. The impregnation time is 2-4 minutes, and this process is repeated 3-4 times to obtain a rough laminate. S4: Pulse hot pressing: Initial stage: the laminate blank is placed at a temperature of 125-135°C, a pressure of 4-6 MPa, and a pulse frequency of 2-4 times / min for 15-20 minutes; Main curing stage: heating to 155-165℃, pressure 10-15MPa, maintaining pressure for 40-50 minutes to obtain semi-finished laminated board; S5: Post-treatment: Roller-coat a water-based flame-retardant coating containing 3wt%-5wt% nano-montmorillonite on the surface of the semi-finished laminate, and cure it at 100-110°C for 2-3 hours to obtain a halogen-free flame-retardant laminated paperboard.

2. The method for preparing the halogen-free flame-retardant phenolic laminated paperboard according to claim 1, characterized in that: In step S1, 0.5wt%-1.5wt% of a polyether-modified silicone defoamer is added to the aqueous emulsion, and the paper base weight is 120-180g / m².

3. The method for preparing the halogen-free flame-retardant phenolic laminated paperboard according to any one of claims 1 or 2, characterized in that: 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.

4. The method for preparing the halogen-free flame-retardant phenolic laminated paperboard according to claim 1, characterized in that: In step S2, 1 wt% to 2 wt% of anatase nano-titanium dioxide with a particle size of 20-50 nm is added to the resin to make the residual carbon rate of the flame retardant resin ≥30%.

5. The method for preparing the halogen-free flame-retardant phenolic laminated paperboard according to claim 1, characterized in that: In step S3, 3 wt% to 8 wt% of a microencapsulated flame retardant with a particle size of 5 to 20 μm is added to the flame retardant resin during the impregnation, wherein the capsule wall of the microencapsulated flame retardant is melamine resin and the core material is ammonium polyphosphate.

6. The method for preparing the halogen-free flame-retardant phenolic laminated paperboard according to any one of claims 1 or 5, characterized in that: In step S3, microwave drying is performed after each immersion, with a microwave power of 600-800 W and a drying time of 40-60 s to make the volatile matter content ≤2.5%.

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

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

9. The method for preparing the 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 diameter of the carbon nanotubes is 10-30nm, the aspect ratio is greater than 100, and the coating resistivity is ≤10 6 Ω·cm.

10. A halogen-free flame-retardant phenolic laminated paperboard, prepared by the method according to any one of claims 1 to 9, characterized in that: (a) Smoke density rating (SDR) ≤ 50; (b) Peak heat release rate ≤ 120 kW / m²; (c) Interface bonding strength ≥ 2.5 MPa.

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