High-strength flame-retardant corrugated board and method for manufacturing the same

Abstract

The present application relates to a kind of high-strength flame-retardant corrugated board and its preparation method.The present application uses dopamine to self-polymerize-wraps ammonium polyphosphate under alkaline conditions, so that the surface of ammonium polyphosphate is aggregated with polydopamine, then by adding silane coupling agent KH-570, so that the alkoxyl of silane coupling agent can and the hydroxyl of polydopamine occur de-alcohol condensation, graft double bond, finally add long-chain alkyl mercaptan as modifier to carry out mercapto-ene click reaction, so that long-chain alkane faces outward, thereby preparing a composite-modified ammonium polyphosphate, so that the coating formed by other components when applied to corrugated board, on the one hand, the accumulation of polydopamine and the grafting of silane coupling agent not only form P-N-Si flame-retardant system, excellent flame-retardant effect, but also form the wrapping structure of organic matter, effectively reduce the migration and precipitation of ammonium polyphosphate, at the same time, by forming long-chain alkane outward hydrophobic structure can also ensure the strength of corrugated board.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of corrugated paperboard, and particularly relates to a high-strength flame-retardant corrugated paperboard and a preparation method thereof. BACKGROUND

[0002] The corrugated paperboard is a multi-layer adhesive body which is composed of at least one corrugated core paper interlayer and one paperboard, has high mechanical strength, and is widely used in packaging, building and other fields, and plays a vital role in human daily life.

[0003] However, since the corrugated paperboard contains a large amount of cellulose and hemicellulose, it has the disadvantage of being flammable, and in order to solve this technical problem, many existing technologies will coat the surface of the corrugated paperboard with a coating containing flame-retardant fillers such as ammonium polyphosphate, so as to endow the corrugated paperboard with excellent flame-retardant performance. However, ammonium polyphosphate has great drawbacks when used as a flame-retardant filler, which limits its actual application effect. On the one hand, ammonium polyphosphate is an inorganic substance, and its compatibility with organic polymers is poor, which is prone to migration and precipitation, thereby causing the flame-retardant effect to decrease. On the other hand, ammonium polyphosphate has a large amount of ammonium salt structure, which makes it easy to absorb water molecules in the air, thereby adversely affecting the strength of the corrugated paperboard itself.

[0004] Therefore, the current corrugated paperboard still has many defects and needs to be improved. SUMMARY

[0005] In view of the problems existing in the prior art, the purpose of the present application is to provide a high-strength flame-retardant corrugated paperboard and a preparation method thereof. In the present application, dopamine is used to self-polymerize and wrap ammonium polyphosphate under alkaline conditions, so that the surface of ammonium polyphosphate is aggregated with polydopamine. Then, silane coupling agent KH-570 is added, so that the alkoxy group of the silane coupling agent can undergo dealcohol condensation with the hydroxyl group of the polydopamine to graft a double bond. Finally, long-chain alkyl mercaptan is added as a modifier to perform a mercapto-alkene click reaction, so that the long-chain alkane faces outward, thereby preparing a composite-modified ammonium polyphosphate. When the coating formed by the composite-modified ammonium polyphosphate and other components is applied to the corrugated paperboard, on the one hand, the accumulation of polydopamine and the grafting of the silane coupling agent not only form a P-N-Si flame-retardant system with excellent flame-retardant effect, but also form a wrapping structure of organic matter, which effectively reduces the migration and precipitation of ammonium polyphosphate. On the other hand, the formation of the hydrophobic structure with the long-chain alkane facing outward can also ensure the strength of the corrugated paperboard.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] A preparation method of a high-strength flame-retardant corrugated paperboard, the preparation method comprising the following steps:

[0008] (1) 120-140 parts by weight of deionized water is added 8-10 parts by weight of ammonium polyphosphate, stirring at room temperature for 5-10 min, then add 6-7 parts by weight of dopamine hydrochloride and 1-2 parts by weight of trimethylamine hydrochloride, stirring at room temperature for 5-10 min, to obtain solution A;

[0009] (2) the pH of solution A is adjusted to 8-9 by using ammonia water, then stirring at room temperature for 40-48 h, centrifugal precipitation, washing with deionized water, and finally vacuum drying at 40-50℃ until constant weight, grinding, to obtain powder A;

[0010] (3) 80-100 parts by weight of ethyl acetate and 2-3 parts by weight of silane coupling agent KH-570 are added to powder A, then stirring at 30-40℃ for 2-3 h, then add 3-4 parts by weight of long-chain alkyl mercaptan and 1-1.5 parts by weight of benzoin dimethyl ether, finally stirring at room temperature for 50-60 min under the irradiation of ultraviolet lamp, filtering, removing the filtrate, washing with ethyl acetate, and vacuum drying at 70-80℃ until constant weight, to obtain composite-modified ammonium polyphosphate;

[0011] (4) 50-60 parts by weight of water-based polyurethane, 0.5-1 parts by weight of dispersant, 0.5-1 parts by weight of film-forming aid and 4-5 parts by weight of composite-modified ammonium polyphosphate are stirred and mixed to obtain a coating;

[0012] (5) the coating is coated on the surface of the corrugated board by using a wire bar coater, and then vacuum drying at 30-40℃ for 24-28 h, to complete the preparation.

[0013] As a preferred technical solution of the present application, the degree of polymerization of the ammonium polyphosphate in step (1) is 1000-1500.

[0014] As a preferred technical solution of the present application, the mass fraction of the ammonia water in step (2) is 5-10%.

[0015] As a preferred technical solution of the present application, the particle size of the powder A in step (2) is 30-40 μm.

[0016] As a preferred technical solution of the present application, the long-chain alkyl mercaptan in step (3) is at least one of dodecyl mercaptan, n-tetradecyl mercaptan, 1-hexadecyl mercaptan and n-octadecyl mercaptan.

[0017] As a preferred technical solution of the present application, the wavelength of the ultraviolet lamp in step (3) is 365 nm.

[0018] As a preferred technical solution of the present application, the solid content of the water-based polyurethane in step (4) is 35-40%.

[0019] As a preferred technical solution of the present application, the dispersant in step (4) is BYK-190 dispersant.

[0020] As a preferred technical solution of the present application, the film forming aid in step (4) is at least one of dodecanol ester and dipropylene glycol butyl ether.

[0021] As a preferred technical solution of the present application, the stirring speed in step (4) is 1000-1500 r / min, and the stirring time is 5-10 min.

[0022] As a preferred technical solution of the present application, the coating thickness in step (5) is 70-80 μm.

[0023] A high-strength flame-retardant corrugated paperboard prepared by the preparation method.

[0024] The beneficial effects of the present application are:

[0025] (1) The present application uses dopamine to self-aggregate and wrap ammonium polyphosphate under alkaline conditions, so that the surface of ammonium polyphosphate is aggregated with polydopamine, then silane coupling agent KH-570 is added, so that the alkoxyl group of the silane coupling agent can undergo dealcohol condensation with the hydroxyl group of the polydopamine to graft a double bond, and finally long-chain alkyl mercaptan is added as a modifier to perform a mercapto-alkene click reaction, so that the long-chain alkane faces outward, thereby preparing a composite-modified ammonium polyphosphate, so that when the coating formed by mixing the composite-modified ammonium polyphosphate with other components is applied to corrugated paperboard, on the one hand, the accumulation of polydopamine and the grafting of silane coupling agent not only form a P-N-Si flame-retardant system with excellent flame-retardant effect, but also form a wrapping structure of organic matter, effectively reducing the migration and precipitation of ammonium polyphosphate, and at the same time, the formation of a long-chain alkane outward hydrophobic structure can also ensure the strength of the corrugated paperboard.

[0026] (2) The present application creatively prepares a composite-modified ammonium polyphosphate, so that when the coating formed by mixing the composite-modified ammonium polyphosphate with other components is actually applied to corrugated paperboard for coating, the polydopamine not only has a large number of benzene ring structures and good carbon formation ability, which can further promote the flame-retardant effect of ammonium polyphosphate, but also can achieve excellent flame-retardant performance without the need for additional flame-retardant fillers after forming the P-N-Si flame-retardant system. DETAILED DESCRIPTION

[0027] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the specific embodiments, structures, features and effects according to the present application are described in detail as follows in combination with examples.

[0028] The corrugated paperboard in the examples and the comparative examples is E-type corrugated paperboard produced by Zhengye Packaging (Zhongshan) Co., Ltd., with a basis weight of 445 g / m 2 .

[0029] Example 1

[0030] A preparation method of high-strength flame-retardant corrugated paperboard, comprising the following steps:

[0031] (1) 8 parts by weight of ammonium polyphosphate is added to 120 parts by weight of deionized water, mixed by stirring at room temperature for 5 min, and then 6 parts by weight of dopamine hydrochloride and 1 part by weight of trimethylamine hydrochloride are added, mixed by stirring at room temperature for 5 min, to obtain solution A;

[0032] (2) The pH of solution A is adjusted to 8 with ammonia water, and then stirred at room temperature for 40 h for reaction, the precipitate is taken by centrifugation, washed with deionized water, and finally vacuum dried at 40°C until constant weight, ground to obtain powder A;

[0033] (3) 80 parts by weight of ethyl acetate and 2 parts by weight of silane coupling agent KH-570 are added to powder A, and then stirred at 30°C for 2 h for reaction, followed by adding 3 parts by weight of long-chain alkyl mercaptan and 1 part by weight of benzoin dimethyl ether, and finally stirring at room temperature for 50 min under the irradiation of an ultraviolet lamp for reaction, filtering, removing the filtrate, washing with ethyl acetate, and vacuum drying at 70°C until constant weight to obtain composite-modified ammonium polyphosphate;

[0034] (4) 50 parts by weight of water-based polyurethane, 0.5 parts by weight of a dispersant, 0.5 parts by weight of a film-forming aid, and 4 parts by weight of the composite-modified ammonium polyphosphate are stirred and mixed to obtain a coating;

[0035] (5) The coating is coated on the surface of the corrugated paperboard by using a wire bar coater, and then vacuum dried at 30°C for 24 h to complete the preparation.

[0036] The polymeric degree of the ammonium polyphosphate in step (1) is 1000.

[0037] The mass fraction of the ammonia water in step (2) is 5%.

[0038] The particle size of the powder A in step (2) is 30 μm.

[0039] The long-chain alkyl mercaptan in step (3) is 1-hexadecane mercaptan.

[0040] The wavelength of the ultraviolet lamp in step (3) is 365 nm.

[0041] The solid content of the water-based polyurethane in step (4) is 35%.

[0042] The dispersant in step (4) is BYK-190 dispersant.

[0043] The film forming aid in step (4) is dodecanol ester.

[0044] The stirring speed in step (4) is 1000 r / min, and the stirring time is 5 min.

[0045] The coating thickness in step (5) is 70 μm.

[0046] A high-strength flame-retardant corrugated paperboard prepared by the preparation method.

[0047] Example 2

[0048] A preparation method of a high-strength flame-retardant corrugated paperboard, comprising the following steps:

[0049] (1) 10 parts by weight of ammonium polyphosphate is added to 140 parts by weight of deionized water, mixed by stirring at room temperature for 10 min, and then 7 parts by weight of dopamine hydrochloride and 2 parts by weight of trimethylamine hydrochloride are added, mixed by stirring at room temperature for 10 min, to obtain solution A;

[0050] (2) The pH of solution A is adjusted to 9 with ammonia water, and then stirred at room temperature for 48 h for reaction, the precipitate is taken by centrifugation, washed with deionized water, and finally dried at 50°C under vacuum until constant weight, ground to obtain powder A;

[0051] (3) 100 parts by weight of ethyl acetate and 3 parts by weight of silane coupling agent KH-570 are added to powder A, stirred at 40°C for 3 h for reaction, then 4 parts by weight of long-chain alkyl mercaptan and 1.5 parts by weight of benzoin dimethyl ether are added, and finally stirred at room temperature for 60 min under the irradiation of ultraviolet lamp for reaction, filtered, the filtrate is removed, washed with ethyl acetate, and dried at 80°C under vacuum until constant weight to obtain composite-modified ammonium polyphosphate;

[0052] (4) 60 parts by weight of water-based polyurethane, 1 part by weight of dispersant, 1 part by weight of film forming aid, and 5 parts by weight of composite-modified ammonium polyphosphate are stirred and mixed to obtain a coating;

[0053] (5) The coating is coated on the surface of the corrugated paperboard by using a wire bar coater, and then dried at 40°C under vacuum for 28 h to complete the preparation.

[0054] The degree of polymerization of ammonium polyphosphate in step (1) is 1500.

[0055] The mass fraction of ammonia water in step (2) is 10%.

[0056] The particle size of powder A in step (2) is 40 μm.

[0057] The long-chain alkyl mercaptan in step (3) is 1-hexadecane mercaptan.

[0058] The wavelength of the ultraviolet lamp in step (3) is 365 nm.

[0059] The solid content of the aqueous polyurethane in step (4) is 40%.

[0060] The dispersant in step (4) is BYK-190 dispersant.

[0061] The film-forming aid in step (4) is dodecanol ester.

[0062] The stirring speed in step (4) is 1500 r / min, and the stirring time is 10 min.

[0063] The thickness of the coating in step (5) is 80 μm.

[0064] A high-strength flame-retardant corrugated paperboard prepared by the preparation method.

[0065] Example 3

[0066] A preparation method of a high-strength flame-retardant corrugated paperboard, comprising the following steps:

[0067] (1) 9 parts by weight of ammonium polyphosphate is added to 130 parts by weight of deionized water, mixed by stirring at room temperature for 8 min, and then 6.5 parts by weight of dopamine hydrochloride and 1.5 parts by weight of trimethylamine hydrochloride are added, mixed by stirring at room temperature for 8 min, to obtain solution A;

[0068] (2) The pH of solution A is adjusted to 8.5 by using ammonia water, and then stirred at room temperature for 44 h for reaction, the precipitate is taken by centrifugation, washed with deionized water, and finally dried at 45°C under vacuum until constant weight, ground, to obtain powder A;

[0069] (3) 90 parts by weight of ethyl acetate and 2.5 parts by weight of silane coupling agent KH-570 are added to powder A, stirred at 35°C for 2.5 h for reaction, then 3.5 parts by weight of long-chain alkyl mercaptan and 1.3 parts by weight of benzoin dimethyl ether are added, and finally stirred at room temperature for 55 min under the irradiation of an ultraviolet lamp for reaction, filtered, the filtrate is removed, washed with ethyl acetate, and dried at 75°C under vacuum until constant weight, to obtain composite-modified ammonium polyphosphate;

[0070] (4) 55 parts by weight of aqueous polyurethane, 0.7 parts by weight of dispersant, 0.8 parts by weight of film-forming aid, and 4.5 parts by weight of composite-modified ammonium polyphosphate are stirred and mixed, to obtain a coating;

[0071] (5) using a wire bar coater to coat the surface of the corrugated paperboard with the coating, and then vacuum drying at 35°C for 26h to complete the preparation.

[0072] The polyphosphoric acid ammonium in step (1) has a degree of polymerization of 1200.

[0073] The mass fraction of the ammonia water in step (2) is 8%.

[0074] The particle size of the powder A in step (2) is 35μm.

[0075] The long-chain alkyl mercaptan in step (3) is 1-hexadecane mercaptan.

[0076] The wavelength of the ultraviolet lamp in step (3) is 365nm.

[0077] The solid content of the water-based polyurethane in step (4) is 38%.

[0078] The dispersant in step (4) is BYK-190 dispersant.

[0079] The film-forming aid in step (4) is dodecanol ester.

[0080] The rotation speed of the stirring in step (4) is 1300r / min, and the stirring time is 8min.

[0081] The thickness of the coating in step (5) is 75μm.

[0082] A high-strength flame-retardant corrugated paperboard prepared by the preparation method.

[0083] Comparative Example 1

[0084] A preparation method of a high-strength flame-retardant corrugated paperboard, comprising the following steps:

[0085] (1) adding 8 parts by weight of polyphosphoric acid ammonium to 120 parts by weight of deionized water, mixing under room temperature for 5min, and then adding 6 parts by weight of dopamine hydrochloride and 1 part by weight of trimethylamine hydrochloride, mixing under room temperature for 5min to obtain solution A;

[0086] (2) adjusting the pH of solution A to 8 by using ammonia water, and then stirring under room temperature for 40h to react, centrifuging to obtain a precipitate, washing with deionized water, and finally vacuum drying at 40°C until constant weight, grinding to obtain powder A;

[0087] (3) adding 80 parts by weight of ethyl acetate and 2 parts by weight of silane coupling agent KH-570 to powder A, stirring at 30°C for 2h to react, filtering to remove the filtrate, washing with ethyl acetate, and vacuum drying at 70°C until constant weight to obtain composite-modified polyphosphoric acid ammonium;

[0088] (4) mixing 50 parts by weight of water-based polyurethane, 0.5 parts by weight of dispersant, 0.5 parts by weight of film-forming aid and 4 parts by weight of the composite-modified ammonium polyphosphate by stirring to obtain a coating material;

[0089] (5) coating the coating material on the surface of the corrugated paperboard by using a wire bar coater, and then drying at 30°C under vacuum for 24h to complete the preparation.

[0090] The polyphosphate ammonium in step (1) has a degree of polymerization of 1000.

[0091] The mass fraction of the ammonia water in step (2) is 5%.

[0092] The particle size of the powder A in step (2) is 30μm.

[0093] The solid content of the water-based polyurethane in step (4) is 35%.

[0094] The dispersant in step (4) is BYK-190 dispersant.

[0095] The film-forming aid in step (4) is dodecanol ester.

[0096] The stirring speed in step (4) is 1000r / min, and the stirring time is 5min.

[0097] The coating thickness in step (5) is 70μm.

[0098] A high-strength flame-retardant corrugated paperboard prepared by the preparation method.

[0099] Comparative Example 2

[0100] A preparation method of a high-strength flame-retardant corrugated paperboard, comprising the following steps:

[0101] (1) adding 8 parts by weight of polyphosphate ammonium to 120 parts by weight of deionized water, mixing by stirring at room temperature for 5min, and then adding 6 parts by weight of dopamine hydrochloride and 1 part by weight of trimethylamine hydrochloride, mixing by stirring at room temperature for 5min to obtain solution A;

[0102] (2) adjusting the pH of solution A to 8 by using ammonia water, and then stirring at room temperature for 40h to react, centrifuging to obtain a precipitate, washing with deionized water, and finally drying under vacuum at 40°C until constant weight, and grinding to obtain powder A;

[0103] (3) mixing 50 parts by weight of water-based polyurethane, 0.5 parts by weight of dispersant, 0.5 parts by weight of film-forming aid and 4 parts by weight of the powder A by stirring to obtain a coating material;

[0104] (4) using a wire bar coater to coat the coating on the surface of the corrugated paperboard, and then vacuum drying at 30°C for 24h, to complete the preparation.

[0105] The polyphosphoric acid ammonium in step (1) has a polymerization degree of 1000.

[0106] The mass fraction of the ammonia water in step (2) is 5%.

[0107] The particle size of the powder A in step (2) is 30μm.

[0108] The solid content of the water-based polyurethane in step (3) is 35%.

[0109] The dispersant in step (3) is BYK-190 dispersant.

[0110] The film-forming aid in step (3) is dodecanol ester.

[0111] The stirring speed in step (3) is 1000r / min, and the stirring time is 5min.

[0112] The thickness of the coating in step (4) is 70μm.

[0113] A high-strength flame-retardant corrugated paperboard prepared by the preparation method.

[0114] Comparative Example 3

[0115] A preparation method of a high-strength flame-retardant corrugated paperboard, comprising the following steps:

[0116] (1) mixing 50 parts by weight of water-based polyurethane, 0.5 parts by weight of dispersant, 0.5 parts by weight of film-forming aid and 4 parts by weight of polyphosphoric acid ammonium by stirring, to obtain a coating;

[0117] (2) using a wire bar coater to coat the coating on the surface of the corrugated paperboard, and then vacuum drying at 30°C for 24h, to complete the preparation.

[0118] The polyphosphoric acid ammonium in step (1) has a polymerization degree of 1000.

[0119] The solid content of the water-based polyurethane in step (1) is 35%.

[0120] The dispersant in step (1) is BYK-190 dispersant.

[0121] The film-forming aid in step (1) is dodecanol ester.

[0122] The stirring speed in step (1) is 1000r / min, and the stirring time is 5min.

[0123] The coating thickness of step (2) is 70 μm.

[0124] A high-strength flame-retardant corrugated paperboard prepared by the preparation method.

[0125] Test Example 1

[0126] Flame-retardant property test:

[0127] The high-strength flame-retardant corrugated paperboards prepared in Examples 1-3 and Comparative Examples 1-3 were respectively subjected to flame-retardant property test (non-washable flame-retardant paper or paperboard) according to the standard GB / T14656-2009. Meanwhile, the high-strength flame-retardant corrugated paperboards were naturally placed (relative humidity 20%) for 90 days and then the above flame-retardant property test was repeated.

[0128] Table 1. Flame-retardant property test results

[0129] Average sustained flaming time / s Average flaming time / s Average char length / mm Example 1 2.8 10.2 18.2 Example 2 2.6 9.4 16.7 Example 3 2.7 9.6 17.5 Comparative Example 1 3.0 10.9 19.1 Comparative Example 2 4.1 14.6 25.3 Comparative Example 3 4.8 20.5 32.4

[0130] Table 2. Flame-retardant property test results (placed for 90 days)

[0131] Average sustained flaming time / s Average flaming time / s Average char length / mm Example 1 2.9 10.6 18.4 Example 2 2.6 9.5 16.9 Example 3 2.7 9.9 18.1 Comparative Example 1 3.3 11.3 19.6 Comparative Example 2 4.5 15.4 26.0 Comparative Example 3 15.4 30.5 105.3

[0132] Test Example 2

[0133] Burst strength test:

[0134] The high-strength flame-retardant corrugated paperboards prepared in Examples 1-3 and Comparative Examples 1-3 were respectively subjected to burst strength test according to the standard GB / T6545-1998 to obtain burst strength A, and then the above burst strength test was repeated after the high-strength flame-retardant corrugated paperboards were naturally placed (relative humidity 80%) for 7 days to obtain burst strength B, and the percentage decrease of burst strength was calculated.

[0135] Table 3. Burst strength test results

[0136] Drop percentage / % Example 1 6.4 Example 2 5.8 Example 3 6.1 Comparative Example 1 9.6 Comparative Example 2 17.7 Comparative Example 3 20.6

[0137] From the comparison of Examples 1-3, Comparative Examples 1-3 and Test Examples 1-2, it can be seen that:

[0138] The difference between Comparative Example 1 and Example 1 is that the long-chain alkane hydrophobic structure is not formed.

[0139] The difference between Comparative Example 2 and Example 1 is that the long-chain alkane hydrophobic structure is not formed, and the silane coupling agent KH-570 is not added for grafting.

[0140] The difference between Comparative Example 3 and Example 1 is that the ammonium polyphosphate is directly used as the flame-retardant filler.

[0141] Compared with the high-strength flame-retardant corrugated paperboard prepared in Embodiments 1-3, Comparative Examples 1-3 and Test Example 1, the high-strength flame-retardant corrugated paperboard prepared in the present application has excellent flame-retardant performance, meanwhile, the composite-modified ammonium polyphosphate is not easy to migrate and precipitate, and has good compatibility with organic polymers.

[0142] Compared with the high-strength flame-retardant corrugated paperboard prepared in Embodiments 1-3, Comparative Examples 1-3 and Test Example 2, the high-strength flame-retardant corrugated paperboard prepared in the present application has good strength, and the composite-modified ammonium polyphosphate is not easy to absorb water molecules in the air, thereby well ensuring the burst strength of the corrugated paperboard.

[0143] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed above with reference to a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any modification, change, equivalent change and modification of the above embodiments, which do not depart from the technical solution of the present application, are still within the scope of the technical solution of the present application.

Claims

1. A process for the preparation of high strength flame retardant corrugated paperboard, characterized by: The preparation method comprises the following steps: (1) adding 8-10 parts by weight of ammonium polyphosphate into 120-140 parts by weight of deionized water, mixing under stirring at room temperature for 5-10 min, then adding 6-7 parts by weight of dopamine hydrochloride and 1-2 parts by weight of trimethylamine hydrochloride, mixing under stirring at room temperature for 5-10 min to obtain solution A; (2) adjusting the pH of solution A to 8-9 by using ammonia water, then stirring at room temperature for 40-48 h to react, centrifuging to obtain a precipitate, washing with deionized water, and finally drying at 40-50 °C under vacuum until constant weight, grinding to obtain powder A; (3) adding 80-100 parts by weight of ethyl acetate and 2-3 parts by weight of silane coupling agent KH-570 into powder A, then stirring at 30-40 °C for 2-3 h to react, then adding 3-4 parts by weight of long-chain alkyl mercaptan and 1-1.5 parts by weight of benzoin dimethyl ether, and finally stirring at room temperature for 50-60 min under irradiation of an ultraviolet lamp to react, filtering to remove the filtrate, washing with ethyl acetate, and drying at 70-80 °C under vacuum until constant weight to obtain composite-modified ammonium polyphosphate; (4) mixing 50-60 parts by weight of waterborne polyurethane, 0.5-1 part by weight of a dispersant, 0.5-1 part by weight of a film-forming aid, and 4-5 parts by weight of the composite-modified ammonium polyphosphate to obtain a coating material; (5) coating the coating material on the surface of a corrugated paperboard by using a wire bar coater, and then drying at 30-40 °C under vacuum for 24-28 h to complete the preparation.

2. A process for the preparation of high strength flame retardant corrugated paperboard as claimed in claim 1, wherein: The ammonium polyphosphate in step (1) has a degree of polymerization of 1000-1500.

3. A process for the preparation of high strength flame retardant corrugated paperboard as claimed in claim 1, wherein: The ammonia water in step (2) has a mass fraction of 5-10%.

4. A process for the preparation of high strength fire retardant corrugated paperboard as claimed in claim 1, wherein: The particle size of powder A in step (2) is 30-40 μm.

5. A process for the preparation of high strength fire retardant corrugated paperboard as claimed in claim 1, wherein: The long-chain alkyl mercaptan in step (3) is at least one of dodecyl mercaptan, n-tetradecyl mercaptan, 1-hexadecyl mercaptan, and n-octadecyl mercaptan.

6. A process for the preparation of high strength fire retardant corrugated paperboard as claimed in claim 1, wherein: The wavelength of the ultraviolet lamp in step (3) is 365 nm.

7. A process for the preparation of high strength fire retardant corrugated paperboard as claimed in claim 1, wherein: The solid content of the waterborne polyurethane in step (4) is 35-40%.

8. A process for the preparation of high strength fire retardant corrugated paperboard as claimed in claim 1, wherein: The film-forming aid in step (4) is at least one of dodecanol ester and dipropylene glycol butyl ether.

9. A process for the preparation of high strength fire retardant corrugated paperboard as claimed in claim 1, wherein: The thickness of the coating in step (5) is 70-80 μm.

10. A high-strength flame-retardant corrugated paperboard prepared by the preparation method of any one of claims 1-9.