Phosphorus-sulfur block unsaturated polyester resin and synthesis method thereof

Abstract

The invention provides phosphorus-sulfur composite flame-retardant block modified unsaturated polyester resin and a synthesis method thereof.The synthesis method includes the steps that after a dichloromethane solution A and a dichloromethane solution B react and are refined, an oligomer C is obtained, then the oligomer C is subjected to ethanol end sealing treatment, an ethanol-terminated oligomer D is obtained, and the phosphorus-sulfur composite flame-retardant block modified unsaturated polyester resin is obtained. The phosphorus-sulfur composite flame-retardant block modified unsaturated polyester resin is obtained by polymerizing and refining the ethanol-terminated oligomer D, the aliphatic diol, the phthalic anhydride, the maleic anhydride and the auxiliary agent, the phosphorus and sulfur element proportion is large, the flame retardant property is good, the content of the phosphorus and sulfur elements in the resin can be accurately controlled in the synthesis stage, and the flame retardant property is good. The diversity and applicability of resin products are improved, the use requirements of different customer groups can be met, the industrialization difficulty is low, the implementation cost is low, and popularization and implementation are convenient.

Description

Technical Field

[0001] The present application belongs to the technical field of chemical raw material production, and specifically relates to a phosphorus-sulfur block unsaturated polyester resin and a synthesis method thereof. Background Art

[0002] In the prior art, flame retardant polymer materials refer to those polymer materials that are not easy to burn or can extinguish themselves when encountering flames. Such materials usually have high thermal stability and good flame retardant properties, and can reduce the burning speed, reduce the possibility of flame propagation, and reduce the release of harmful smoke and gas in a fire. The application of flame retardant polymer materials is very wide, including construction, transportation, electronics and electrical, and aerospace. In recent years, fires have become more and more frequent, and the economic losses caused by fires have become more and more serious;

[0003] In the prior art, the polymer materials widely used in daily life generally have a limiting oxygen index of 17%-20% and are flammable. The existing flame retardant modification methods for polymer materials are usually physical modifications, that is, halogen flame retardants are mixed into the resin matrix. In the actual implementation process, due to the mixing of halogen flame retardants, polymer materials will produce a large amount of toxic gases and smoke during the combustion process. With the advancement of science and technology and the improvement of people's environmental awareness, a number of environmental protection laws and regulations have been promulgated. Halogen flame retardants are currently on the verge of being eliminated and do not conform to the scientific concept of green chemistry. On the other hand, after the polymer material is mixed with halogen flame retardants, filler migration and agglomeration will occur during long-term use, which will not only cause the flame retardant component to fail, significantly reduce the flame retardant properties of the resin, but also reduce the mechanical properties of the resin system. Therefore, improvements are urgently needed. Summary of the invention

[0004] In order to solve the technical problem that the polymer materials widely used in daily life in the prior art generally have a limiting oxygen index of 17%-20%, are highly thermally sensitive, and are easily burned when encountering a fire source, on the one hand, there are great safety hazards, and they need to be flame-retardantly modified to meet the needs of users, and on the other hand, the existing flame retardants are mostly halogen flame retardants, and are mostly mixed into the resin matrix in the form of fillers, the resin system has poor stability, and a large amount of toxic gases will be generated during the combustion of the resin, which does not conform to the concept of green chemistry, and a phosphorus-sulfur block unsaturated polyester resin is proposed;

[0005] In order to solve the technical problem raised in the present application, the present application also provides a method for preparing a phosphorus-sulfur block unsaturated polyester resin.

[0006] The present application adopts the following scheme, a method for synthesizing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin, comprising the following steps:

[0007] Step 101. After dichloromethane solution A is dropped into dichloromethane solution B, the mixture is reacted for 1 h to 3 h in a water bath at 50° C. to 70° C. and 500 rpm to 1200 rpm to obtain a crude oligomeric product C;

[0008] Wherein, dichloromethane solution A is a dichloromethane solution of methylphosphoryl dichloride, and dichloromethane solution B is a dichloromethane solution of 4,4'-diaminodiphenyl sulfone and triethylamine;

[0009] Step 102. The crude oligomer C obtained after filtering the liquid phase in step 101 is washed with dilute hydrochloric acid, sodium bicarbonate solution, saturated concentrated brine and deionized water in sequence, and then evaporated to dryness to obtain oligomer C;

[0010] Step 103. The oligomer C obtained in step 102 is dispersed in 2-bromoethanol, and an aqueous solution of ethylene glycol is added dropwise thereto. The mixture is reacted for 1 h to 10 h in a water bath at 70° C. to 90° C., then cooled to room temperature, and a 10% sodium hydroxide solution is added to precipitate the product, thereby obtaining an ethanol-terminated oligomer D.

[0011] Step 104. Add the ethanol-terminated oligomer D, fatty diol, phthalic anhydride, maleic anhydride and additives prepared in step 103 into a reactor, and react for 15h-20h at 150°C-220°C in an inert gas environment to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin semi-finished product, and then transfer it to a dilution kettle for dilution, and then filter and package it in turn to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin finished product.

[0012] In one embodiment, in step 101, the dichloromethane solution A is a solution prepared by mixing methylphosphoryl dichloride and dichloromethane solution in a mass ratio of 4:5;

[0013] The dichloromethane solution B is a solution prepared by mixing 4,4'-diaminodiphenyl sulfone, triethylamine and dichloromethane solution in a mass ratio of 4:3:5.

[0014] In the actual implementation process, if it is necessary to adjust the proportion of phosphorus-sulfur elements in the resin, for example, if the phosphorus ratio needs to be increased, part of the 4,4'-diaminodiphenyl sulfone can be replaced with ethylenediamine or benzidine, and if the sulfur ratio needs to be increased, methyl phosphoryl dichloride can be replaced with terephthaloyl chloride, etc. The unsaturated polyester resin prepared by this scheme has a large proportion of phosphorus and sulfur in the chain segments, has good flame retardant properties, and its proportion can be accurately adjusted in the synthesis stage to obtain a series of unsaturated polyester resins with different flame retardant properties and flame retardant characteristics, so as to meet the flame retardant requirements of different resin products and improve the applicability of phosphorus-sulfur composite flame retardant block-modified unsaturated polyester resins.

[0015] In the actual implementation process, the by-product sodium bromide and the ethylene glycol / diethylene glycol mixture in steps 101 to 104 can be sold separately after being separated by distillation, which significantly improves the utilization rate of the reactants.

[0016] In one embodiment, in step 102, the structural formula of oligomer C is as follows:

[0017]

[0018] The value range of n is 1500-2650.

[0019] The synthesis method of oligomer C in step 102 is as follows:

[0020]

[0021] In one embodiment, in step 103, under a nitrogen atmosphere, the oligomer C obtained in step 102 is dispersed in 2-bromoethanol at a molar ratio of 1:1, and then an aqueous solution of ethylene glycol is added dropwise thereto. During the reaction, the concentration of 2-bromoethanol is monitored by HPLC.

[0022] In one embodiment, in step 103, during the reaction of oligomer C, the concentration of 2-bromoethanol is monitored by HPLC, and the molar ratio of ethylene glycol to oligomer C is maintained at 1.05-1.1:1.

[0023] In one embodiment, in step 103, the structural formula of the ethanol-terminated oligomer D is as follows:

[0024]

[0025] The value range of n is 1680-2100.

[0026] In step 103, the synthesis equation of the ethanol-terminated oligomer D is as follows:

[0027]

[0028] In the actual implementation process, during the preparation of oligomer C in step 102, oligomer C may contain two terminal groups, one of which is a phosphorus oxychloride group and the other is a primary amine. The amino group can be converted into an N-ethanol group through the substitution reaction of bromoethanol and the primary amine; the phosphorus oxychloride can be converted into a hydroxyl phosphate through the alcoholysis of ethylene glycol and acyl chloride, thereby converting both terminal groups into hydroxyl groups, and then preparing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin by addition polymerization, which can effectively protect the phosphorus and sulfur elements in the resin and improve the flame retardant properties of the resin system.

[0029] In one embodiment, in step 104, the molar ratio of ethanol-terminated oligomer D, aliphatic diol, phthalic anhydride, and maleic anhydride is 1.05:1.25:1.15:1.

[0030] In one embodiment, in step 104, during the reaction, samples are taken from the reaction system every 30 minutes to detect the acid value in the system. When the acid value of the reaction system reaches 30 mgKOH / g, the reaction system is cooled to 90° C. and the reaction is terminated.

[0031] In order to solve the technical problem raised by the present application, the present application also provides a phosphorus-sulfur composite flame retardant block modified unsaturated polyester resin, which is prepared by the above-mentioned synthesis method of a phosphorus-sulfur composite flame retardant block modified unsaturated polyester resin.

[0032] In one embodiment, the phosphorus-sulfur composite flame retardant block-modified unsaturated polyester resin has the following structural formula:

[0033]

[0034] Among them, the value range of m is 1800-3500, and the value range of n is 1800-2000.

[0035] Compared with the prior art, this application has the following beneficial effects:

[0036] The present application provides a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin and a synthesis method thereof. The resin is prepared by reacting a dichloromethane solution A with a dichloromethane solution B and refining the resultant to obtain an oligomer C. The oligomer C is then subjected to an ethanol end-capping treatment to obtain an ethanol-end-capped oligomer D. Finally, the ethanol-end-capped oligomer D, a fatty diol, phthalic anhydride, maleic anhydride and an auxiliary agent are polymerized and refined to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin. The phosphorus and sulfur elements account for a relatively large proportion of the resin, and the resin has excellent flame-retardant properties. The content of the phosphorus and sulfur elements in the resin can be accurately controlled in the synthesis stage, thereby improving the diversity and applicability of the resin product, and meeting the use requirements of different customer groups. The resin has the advantages of low industrialization difficulty, low implementation cost, and easy promotion and implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the 1H NMR spectrum of oligomer C prepared in Example 3 of the present application;

[0038] Figure 2 This is the 13C NMR spectrum of oligomer C prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0039] The present technical solution is further explained in combination with Examples 1-3.

[0040] Example 1

[0041] (1) The method for synthesizing phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin comprises the following steps:

[0042] Step 101. After dichloromethane solution A is dropped into dichloromethane solution B, the mixture is reacted for 1 hour in a water bath at 69.5° C. and 750 rpm to obtain a crude oligomeric product C;

[0043] Wherein, the dichloromethane solution A is a solution prepared by mixing methylphosphoryl dichloride and dichloromethane solution in a mass ratio of 4:5;

[0044] Dichloromethane solution B is a solution prepared by mixing 4,4'-diaminodiphenyl sulfone, triethylamine and dichloromethane solution in a mass ratio of 4:3:5;

[0045] Step 102. The crude oligomer C obtained after filtering the liquid phase in step 101 is washed with dilute hydrochloric acid, sodium bicarbonate solution, saturated concentrated brine and deionized water in sequence, and then evaporated to dryness to obtain oligomer C;

[0046] Step 103. Under a nitrogen atmosphere, the oligomer C obtained in step 102 is dispersed in 2-bromoethanol at a molar ratio of 1:1, and then an aqueous solution of ethylene glycol is added dropwise thereto. During the reaction, the concentration of 2-bromoethanol is monitored by HPLC in a water bath at 70° C. to maintain the molar ratio of ethylene glycol to oligomer C at 1.05:1. After reacting for 8.5 hours, the mixture is cooled to room temperature, and a 10% sodium hydroxide solution is added to precipitate the product, thereby obtaining an ethanol-terminated oligomer D.

[0047] Step 104. Add the ethanol-terminated oligomer D, fatty diol, phthalic anhydride, maleic anhydride and auxiliary agent prepared in step 103 into a reactor, and react for 19 hours at 157° C. in a nitrogen atmosphere. During the reaction, take samples from the reaction system every 30 minutes to detect the acid value in the system. When the acid value of the reaction system reaches 30 mgKOH / g, cool the reaction system to 90° C. and terminate the reaction to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin semi-finished product. Then transfer it to a dilution kettle for dilution, filter it, and package it to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin finished product.

[0048] The molar ratio of ethanol-terminated oligomer D, aliphatic diol, phthalic anhydride and maleic anhydride is 1.05:1.25:1.15:1.

[0049] Example 2

[0050] (1) The method for synthesizing phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin comprises the following steps:

[0051] Step 101. After dichloromethane solution A is dropped into dichloromethane solution B, the mixture is reacted for 2 hours in a water bath at 60° C. and 500-1200 rpm to obtain a crude oligomeric product C;

[0052] Wherein, the dichloromethane solution A is a solution prepared by mixing methylphosphoryl dichloride and dichloromethane solution in a mass ratio of 4:5;

[0053] Dichloromethane solution B is a solution prepared by mixing 4,4'-diaminodiphenyl sulfone, triethylamine and dichloromethane solution in a mass ratio of 4:3:5;

[0054] Step 102. The crude oligomer C obtained after filtering the liquid phase in step 101 is washed with dilute hydrochloric acid, sodium bicarbonate solution, saturated concentrated brine and deionized water in sequence, and then evaporated to dryness to obtain oligomer C;

[0055] Step 103. Under a nitrogen atmosphere, the oligomer C obtained in step 102 is dispersed in 2-bromoethanol at a molar ratio of 1:1, and then an aqueous solution of ethylene glycol is added dropwise thereto. Under the condition of 80° C. in a water bath, the concentration of 2-bromoethanol is monitored by HPLC during the reaction to maintain the molar ratio of ethylene glycol to oligomer C at 1.07:1. After reacting for 5 hours, the mixture is cooled to room temperature, and a 10% sodium hydroxide solution is added to precipitate the product, thereby obtaining an ethanol-terminated oligomer D;

[0056] Step 104. Add the ethanol-terminated oligomer D, fatty diol, phthalic anhydride, maleic anhydride and auxiliary agent prepared in step 103 into a reactor, and react for 18 hours at 185° C. in a nitrogen atmosphere. During the reaction, take samples from the reaction system every 30 minutes to detect the acid value in the system. When the acid value of the reaction system reaches 30 mgKOH / g, cool the reaction system to 90° C., terminate the reaction, and obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin semi-finished product. Then transfer it to a dilution kettle for dilution, filter it, and package it to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin finished product.

[0057] The molar ratio of ethanol-terminated oligomer D, aliphatic diol, phthalic anhydride and maleic anhydride is 1.05:1.25:1.15:1.

[0058] Example 3

[0059] (1) The method for synthesizing phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin comprises the following steps:

[0060] Step 101. After dichloromethane solution A is dropped into dichloromethane solution B, the mixture is reacted for 3 hours in a water bath at 55° C. and 1200 rpm to obtain a crude oligomeric product C;

[0061] Wherein, the dichloromethane solution A is a solution prepared by mixing methylphosphoryl dichloride and dichloromethane solution in a mass ratio of 4:5;

[0062] Dichloromethane solution B is a solution prepared by mixing 4,4'-diaminodiphenyl sulfone, triethylamine and dichloromethane solution in a mass ratio of 4:3:5;

[0063] Step 102. The crude oligomer C obtained after filtering the liquid phase in step 101 is washed with dilute hydrochloric acid, sodium bicarbonate solution, saturated concentrated brine and deionized water in sequence, and then evaporated to dryness to obtain oligomer C;

[0064] Step 103. Under a nitrogen atmosphere, the oligomer C obtained in step 102 is dispersed in 2-bromoethanol at a molar ratio of 1:1, and then an aqueous solution of ethylene glycol is added dropwise thereto. During the reaction, the concentration of 2-bromoethanol is monitored by HPLC in a water bath at 90° C. to maintain the molar ratio of ethylene glycol to oligomer C at 1.1:1. After reacting for 2.5 hours, the mixture is cooled to room temperature, and a 10% sodium hydroxide solution is added to precipitate the product, thereby obtaining an ethanol-terminated oligomer D;

[0065] Step 104. Add the ethanol-terminated oligomer D, fatty diol, phthalic anhydride, maleic anhydride and auxiliary agent prepared in step 103 into a reactor, and react for 15 hours at 220° C. in a nitrogen atmosphere. During the reaction, take samples from the reaction system every 30 minutes to detect the acid value in the system. When the acid value of the reaction system reaches 30 mgKOH / g, cool the reaction system to 90° C. and terminate the reaction to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin semi-finished product. Then transfer it to a dilution kettle for dilution, filter it, and package it to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin finished product.

[0066] The molar ratio of ethanol-terminated oligomer D, aliphatic diol, phthalic anhydride and maleic anhydride is 1.05:1.25:1.15:1.

[0067] The phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin prepared in Examples 1-3 was subjected to the following tests:

[0068] Test 1: The phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resins prepared in Examples 1-3 were sampled respectively, and after being made into test pieces of the same specifications, the corresponding limiting oxygen indexes were measured respectively;

[0069] Test 2: The phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resins prepared in Examples 1-3 were sampled, and after being made into test pieces of the same specifications, their corresponding UL-94 flame retardancy ratings were measured respectively;

[0070] Test 3: Stability test, the phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin prepared in Examples 1-3 was left to stand and aged, and then made into test pieces of the same specifications, and the corresponding UL-94 flame retardancy ratings were measured respectively;

[0071] The aging treatment includes placing the phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin prepared in Examples 1-3 in an environment of 50° C. for 24 hours, 72 hours and 120 hours, and then measuring its corresponding UL-94 flame retardancy rating. The test results are shown in Table 1 below.

[0072] Table 1 Test results of Examples 1-3

[0073]

[0074] From the test results table 1 above and Figure 1-Figure 2 It can be seen that the phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin prepared in Examples 1-3 has a high sulfur and phosphorus content, excellent flame retardant performance, excellent anti-aging performance, and can still maintain excellent flame retardant performance after being placed for a long time. Under storage conditions with high temperature, the phosphorus and sulfur elements in the unsaturated polyester resin will not be stored in stages, the flame retardant performance will not decrease, and it has extremely high thermal stability;

[0075] The dichloromethane solution A is reacted with the dichloromethane solution B and then refined to obtain oligomer C, which is then end-capped with ethanol to obtain ethanol-end-capped oligomer D, and finally the ethanol-end-capped oligomer D, aliphatic diol, phthalic anhydride, maleic anhydride and an auxiliary agent are polymerized and refined to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin, in which phosphorus and sulfur elements account for a large proportion and have good flame retardant properties. The content of phosphorus and sulfur elements in the resin can be accurately controlled in the synthesis stage, thereby improving the diversity and applicability of the resin product and meeting the use needs of different customer groups. The industrialization difficulty is low, the implementation cost is low, and it is easy to promote and implement.

[0076] The above are only embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for synthesizing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin, characterized in that: The following steps are involved: Step 101. After dichloromethane solution A is dropped into dichloromethane solution B, the mixture is reacted for 1 h to 3 h in a water bath at 50° C. to 70° C. and 500 rpm to 1200 rpm to obtain a crude oligomeric product C; Wherein, dichloromethane solution A is a dichloromethane solution of methylphosphoryl dichloride, and dichloromethane solution B is a dichloromethane solution of 4,4'-diaminodiphenyl sulfone and triethylamine; Step 102. The crude oligomer C obtained after filtering the liquid phase in step 101 is washed with dilute hydrochloric acid, sodium bicarbonate solution, saturated concentrated brine and deionized water in sequence, and then evaporated to dryness to obtain oligomer C; Step 103. The oligomer C obtained in step 102 is dispersed in 2-bromoethanol, and an aqueous solution of ethylene glycol is added dropwise thereto. The mixture is reacted for 1 h to 10 h in a water bath at 70° C. to 90° C., and then cooled to room temperature. A 10% sodium hydroxide solution is added to precipitate the product, thereby obtaining an ethanol-terminated oligomer D. Step 104. Add the ethanol-terminated oligomer D, fatty diol, phthalic anhydride, maleic anhydride and additives prepared in step 103 into a reactor, and react for 15h-20h at 150°C-220°C in an inert gas environment to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin semi-finished product, and then transfer it to a dilution kettle for dilution, and then filter and package it in turn to obtain a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin finished product.

2. The method for synthesizing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin according to claim 1, characterized in that: In step 101, the dichloromethane solution A is a solution prepared by mixing methylphosphoryl dichloride and dichloromethane solution in a mass ratio of 4:5; The dichloromethane solution B is a solution prepared by mixing 4,4'-diaminodiphenyl sulfone, triethylamine and dichloromethane solution in a mass ratio of 4:3:

5.

3. The method for synthesizing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin according to claim 1, characterized in that: In step 102, the structural formula of oligomer C is as follows: The value range of n is 1500-2650.

4. The method for synthesizing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin according to claim 1, characterized in that: In step 103, under a nitrogen atmosphere, the oligomer C obtained in step 102 is dispersed in 2-bromoethanol at a molar ratio of 1:1, and then an aqueous solution of ethylene glycol is added dropwise thereto. During the reaction, the concentration of 2-bromoethanol is monitored by HPLC.

5. The method for synthesizing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin according to claim 1, characterized in that: In step 103, during the reaction of oligomer C, the concentration of 2-bromoethanol is monitored by HPLC, and the molar ratio of ethylene glycol to oligomer C is maintained at 1.05-1.1:

1.

6. The method for synthesizing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin according to claim 1, characterized in that: In step 103, the structural formula of the ethanol-terminated oligomer D is as follows: The value range of n is 1680-2100.

7. The method for synthesizing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin according to claim 1, characterized in that: In step 104, the molar ratio of ethanol-terminated oligomer D, aliphatic diol, phthalic anhydride, and maleic anhydride is 1.05:1.25:1.15:

1.

8. The method for synthesizing a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin according to claim 1, characterized in that: In step 104, during the reaction, samples are taken from the reaction system every 30 minutes to detect the acid value in the system. When the acid value of the reaction system reaches 30 mgKOH / g, the reaction system is cooled to 90° C. and the reaction is terminated.

9. A phosphorus-sulfur composite flame retardant block-modified unsaturated polyester resin, characterized in that: The invention is prepared by the synthesis method of a phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin as described in any one of claims 1 to 8.

10. A phosphorus-sulfur composite flame-retardant block-modified unsaturated polyester resin according to claim 9, characterized in that: Its structural formula is as follows: Among them, the value range of m is 1800-3500, and the value range of n is 1800-2000.

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