1. A preparation method of melamine cyanurate is characterized by comprising the following steps:

1) preparation of melamine cyanurate slurry: uniformly mixing melamine and cyanuric acid, adding a modification auxiliary agent and deionized water, and reacting to obtain melamine cyanurate slurry;

2) aqueous hydrothermal method: inputting the melamine cyanurate slurry obtained in the step 1) into a reaction kettle, adding deionized water and the mother liquor recycled in the step 3), stirring, continuing to react completely, controlling the viscosity through the reaction time in the reaction process, discharging after the viscosity is stable, reducing the particle size tailing and increasing the decomposition temperature;

3) filtering and pre-drying: filtering the reaction liquid in the reaction kettle in the step 2), recycling mother liquor, and pre-drying the filtered material;

4) crushing and drying: crushing the material pre-dried in the step 3), and performing secondary drying to obtain the product melamine cyanurate.

2. The method for preparing melamine cyanurate according to claim 1, wherein in step 1), the molar ratio of melamine to cyanuric acid is 1:0.95-1.05, the conductivity of deionized water is less than or equal to 5 μ s/cm, the amount of deionized water added is 5-30 wt% of the total weight of melamine and cyanuric acid, the reaction temperature is 60-95 ℃, and the reaction time is 0.5-3 h.

3. The method according to claim 1, wherein the amount of the mother liquor and the deionized water added in step 2) is 2-5 times the weight of the melamine cyanurate slurry.

4. The method as claimed in claim 1, wherein the temperature of the further reaction in step 2) is 60-95 ℃, the reaction time is 50-100min, and the viscosity of the reaction solution is controlled to 100-150 cP.

5. The method according to claim 1, wherein the moisture content of the pre-dried material in step 3) is less than or equal to 2%.

6. The method according to claim 1, wherein the temperature of the secondary drying in step 4) is 120-300 ℃.

7. The method for preparing melamine cyanurate according to any one of claims 1-6, characterized in that the modifying assistant comprises one or more of alcohols, pyrophosphates or silicon-oxygen compounds, and the amount of the modifying assistant added is 0.01-0.5% of the total weight of melamine and cyanuric acid.

8. Melamine cyanide obtainable by the process according to any one of claims 1 to 7Use of urate, characterized in that melamine cyanurate is used for spinning or flame-retardant modification, the melamine cyanurate having a particle size D₁₀₀Less than 5 μm, and 0.5% mass loss temperature more than or equal to 305 ℃.

9. Use of melamine cyanurate according to claim 8, characterised in that the spinning medium is nylon, in weight%: 4 to 15 percent of melamine cyanurate, 0.05 to 5 percent of lubricant, 0.05 to 6 percent of cyclic phosphate, 0.05 to 0.5 percent of antioxidant 1098, and the balance of nylon chips.

10. The use of melamine cyanurate according to claim 8, wherein the spinning medium is dacron, and the following components are present in weight percent: 1-10% of melamine cyanurate, 0.05-5% of lubricant, 0.05-6% of organic hypophosphite, 0.05-0.5% of antioxidant and the balance of PET chips.

Background

Melamine cyanurate, MCA for short, the Chinese name melamine cyanurate, the molecular formula C₆H₉N₉0₃The product is white crystal powder, non-toxic, odorless, insoluble in water, soluble in organic solvents such as ethanol and formaldehyde, weakly acidic, and stable in chemical property. MCA has the advantages of no halogen, low toxicity, low smoke and the like, belongs to an environment-friendly flame retardant, can be used for flame retarding of polymers such as polyamide, polyester, polyolefin, epoxy resin, polyurethane and the like, is particularly suitable for flame retarding polyamide materials, and has the characteristics of no halogen, low toxicity, environment friendliness and the like. Furthermore, MCA has excellent solid lubrication effect and can be used in cosmetics.

At present, the melamine cyanuric acid is industrially produced mainly by adopting an atmospheric pressure liquid phase method and a solid-phase slurry method, the atmospheric pressure liquid phase method is used for reacting melamine and cyanuric acid in a water phase according to a certain proportion to prepare the melamine cyanuric acid, the product has high viscosity, the content is about 10 percent generally, the filtration is difficult, the water consumption of unit products is high, the utilization rate of a reactor is low, the energy consumption is high, the product has large particle size, the particle size is trailing, the products exist in an agglomeration form, the phenomena of screen blockage, white spots and the like are easily caused in the polymer spinning or extrusion process, the thermal stability of the product is poor, and the requirements of the polymer spinning can not be met for a long time.

Chinese patents CN101037417A, CN103073515A, CN103059337A and the like applied by Hangzhou Jieisi flame-retardant chemical company Limited are prepared by a solid-phase slurry method, so that the water consumption for producing melamine cyanuric acid is reduced, the purity and the thermal stability of the melamine cyanuric acid are ensured, the particle size of the product is adjusted by a crushing process, and the product has coarse particle size and wide distribution, but the improvement on the dispersibility is not obvious.

Therefore, reducing tailing of melamine cyanurate, improving thermal stability of the product, and improving dispersibility are one of the important research directions for widening the application field of melamine cyanurate.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a preparation method of melamine cyanurate with reduced particle size tailing and high thermal stability, the melamine cyanurate and application thereof. And the tailing of the particle size is regulated and controlled according to the viscosity during the second-step synthesis, so that the problem that the tailing of the particle size cannot be ensured by a crushing process of the conventional commercially available flame retardant is solved, and the adverse phenomena of particle agglomeration, dispersion and the like are improved by the aid of the aid.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of melamine cyanurate comprises the following steps:

1) preparation of melamine cyanurate slurry: uniformly mixing melamine and cyanuric acid, adding a modification auxiliary agent and deionized water, and reacting to obtain melamine cyanurate slurry;

2) aqueous hydrothermal method: inputting the melamine cyanurate slurry obtained in the step 1) into a reaction kettle, adding deionized water and the mother liquor recycled in the step 3), stirring, continuing to react completely, controlling the viscosity through the reaction time in the reaction process, discharging after the viscosity is stable, reducing the particle size tailing and increasing the decomposition temperature;

3) filtering and pre-drying: filtering the reaction liquid in the reaction kettle in the step 2), recycling mother liquor, and pre-drying the filtered material;

4) crushing and drying: crushing the material pre-dried in the step 3), and performing secondary drying to obtain the product melamine cyanurate.

In the technical scheme, the invention adopts a semi-solid heat method combining a solid-phase slurry method and a water-phase hydrothermal method, the process comprises two steps of preparing melamine cyanurate, and the first step of preparing melamine cyanurate by using the solid-phase slurry methodSlurry, which adds modifying assistant to improve flow property and dispersing property; the second step is a water-phase hydrothermal method for further finishing the reaction, the conventional hydrothermal method is used for reacting MCA, the concentration of reactants is about 9 wt%, the system viscosity is over 600cP, and large particles formed by hydrogen bonds cannot be prevented due to less viscosity and large shearing effect of the reactants, and D₁₀₀Not less than 10 μm. When the reaction time is shorter, the system viscosity is lower, the shearing is weakened, and D₁₀₀Will also increase. According to the invention, as the first step of solid-phase slurry reaction is carried out, the salt forming reaction is basically completed, the particles are formed, the aqueous phase hydrothermal method ensures complete completion of the salt forming reaction and complete crystallization in an aqueous medium, the defect of rapid increase of viscosity in a single aqueous phase method is avoided, the reaction can be carried out at a higher reaction viscosity, the viscosity is controlled by controlling the reaction time in the process, the system viscosity is in a proper range, the stirring shearing force is ensured, the macromolecular three-dimensional network structure formed by MCA due to hydrogen bonds is prevented, secondary aggregation particles are effectively prevented from thickening, and the D of the product is ensured₁₀₀Fine grain size, reduced grain size tailing.

The invention prepares the MCA with less grain diameter tailing and high thermal stability by a two-step method, solves the problem that the grain diameter tailing of the traditional commercially available flame retardant cannot be ensured by a crushing process, and simultaneously improves the phenomena of particle agglomeration, poor dispersion and the like of the MCA caused by stronger hydrogen bond action. The product prepared by the invention has the advantages of excellent thermal stability, good compatibility in polymers, no precipitation, good dispersion, no white point and the like.

The invention solves the problems of low production efficiency and large water consumption of the traditional aqueous phase method, because the melamine and the cyanuric acid are mutually combined by intermolecular hydrogen bond acting force, a three-dimensional network structure is gradually formed by the action of hydrogen bonds in the reaction process, the viscosity rises suddenly, the content of reactants can only reach about 9 percent, and the production efficiency is low. The invention finishes most of reactions when preparing the slurry initial product, has no viscosity suddenly rising in the water phase, the solid content of reactants can reach 20 percent, the production efficiency is high, and the viscosity change in the reaction process of the two preparation methods is shown in figure 1.

As a preferable scheme of the invention, the mol ratio of the melamine to the cyanuric acid in the step 1) is 1:0.95-1.05, the conductivity of the deionized water is less than or equal to 5 mu s/cm, the addition amount of the deionized water is 5-30 wt% of the total weight of the melamine and the cyanuric acid, the reaction temperature is 60-95 ℃, and the reaction time is 0.5-3 h.

In a preferred embodiment of the present invention, in step 2), the mother liquor and deionized water are added in an amount of 2 to 5 times the weight of the melamine cyanurate slurry.

As a preferable scheme of the invention, in the step 2), the temperature of the further reaction is 60-95 ℃, the reaction time is 50-100min, and the viscosity of the reaction solution is controlled to be 100-150 cP.

As a preferable scheme of the invention, in the step 3), the moisture content of the pre-dried material is less than or equal to 2%.

As a preferable scheme of the invention, in the step 4), the temperature of the secondary drying is 120-300 ℃.

As a preferable scheme of the invention, the modification auxiliary agent comprises one or more of alcohol substances, pyrophosphate or silicon-oxygen compounds, and the addition amount of the modification auxiliary agent is 0.01-0.5% of the total weight of melamine and cyanuric acid.

The application of the melamine cyanurate prepared by the preparation method, the application of the melamine cyanurate in spinning or flame-retardant modification, and the particle size D of the melamine cyanurate₁₀₀Less than 5 μm, and 0.5% mass loss temperature more than or equal to 305 ℃.

As a preferred scheme of the invention, the spinning carrier is nylon, and the weight percentages are as follows: 4 to 15 percent of melamine cyanurate, 0.05 to 5 percent of lubricant, 0.05 to 6 percent of cyclic phosphate, 0.05 to 0.5 percent of antioxidant 1098, and the balance of nylon chips.

As a preferred scheme of the invention, the spinning carrier is terylene, and the carrier comprises the following components in percentage by weight: 1-10% of melamine cyanurate, 0.05-5% of lubricant, 0.05-6% of organic hypophosphite, 0.05-0.5% of antioxidant and the balance of PET chips.

Compared with the prior art, the invention has the following beneficial effects:

1. according to the invention, a semi-solid-heat method preparation technology combining a solid phase method and a water phase method is adopted, and through a two-step preparation method, the trailing of the particle size is regulated and controlled according to the viscosity during synthesis, so that the problem that the trailing of the particle size cannot be ensured by depending on a crushing process of the conventional commercially available flame retardant is solved, and the phenomena of easy particle agglomeration, poor dispersion and the like are improved;

2. the invention solves the problems of low production efficiency and large water consumption of the traditional aqueous phase method, because the melamine and the cyanuric acid are mutually combined through intermolecular hydrogen bond acting force, a three-dimensional network structure can be formed to expand towards each direction when the reaction reaches a certain degree, so that the viscosity rises suddenly, the content of reactants can only reach about 9 percent, and the production efficiency is low, but the invention finishes most of salt forming reaction because of the first step of solid-phase slurry preparation in a reactor, the condition of sudden rise of the viscosity does not exist in the aqueous phase, the solid content of the reactants can reach 20 percent, and the production efficiency is high;

3. the invention solves the problems that MCA is easy to agglomerate and block a screen because of fine particle size, and the added modification auxiliary agent comprises one or more of alcohols, pyrophosphate or silicon oxide, the addition amount of the modification auxiliary agent is 0.01-2% of the total weight of MCA, so that the compatibility of MCA and the polymer is improved, and the dispersibility of the product is improved.

Drawings

FIG. 1 is a graph showing the change of viscosity with time during the reaction of the aqueous phase method and the semi-solid heat method.

FIG. 2 is a graph of the spinning morphology of melamine cyanurate in PA as prepared in example 1.

FIG. 3 is a graph of the spinning topography of melamine cyanurate in PA as obtained in comparative example 1.

FIG. 4 is a graph of the spinning topography of melamine cyanurate in PA as obtained in comparative example 2.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The methods of viscosity test and particle size test performed in the present invention are as follows:

viscosity test, Brookfield/DV2T rotary viscometer, HB-06 rotor, 90 deg.C, 25rpm, viscosity of MCA reaction system, viscosity unit is cP.

And (3) testing the particle size, namely using an Oumei gram/POP (6) laser particle size analyzer to take a proper amount of MC sample into a 10mL measuring cup, adding about 8-10 mL of alcohol, stirring, performing ultrasonic treatment for 2 minutes, pouring into a sample pool, wherein the concentration is ensured to be between 8 and 13 of shading ratio.

Example 1

1) Preparation of melamine cyanurate slurry: 370kg of melamine (with the purity of 99.5%) and 374kg of cyanuric acid (with the purity of 98.5%) are added into a 2000L horizontal reactor, mixed for 30 minutes, added with fumed nano-silica with the weight of 1kg, stirred for 30 minutes, added with 100kg of deionized water (the conductivity is less than or equal to 5 mus/cm), and continuously stirred for 40 minutes to be uniformly mixed. Heating while stirring, and keeping at 80 ℃ for 1.5 hours to obtain a melamine cyanurate slurry primary product;

2) aqueous hydrothermal method: inputting the melamine cyanurate slurry obtained in the step 1) into a 5000L reaction kettle, adding 3000L mother liquor and deionized water (the balance is complemented by the deionized water), heating and stirring at the temperature of 90 ℃, discharging for 1 hour, and discharging with the viscosity of 127 cP;

3) filtering and pre-drying: filtering the materials by a centrifugal machine, inputting filter cakes into a flash evaporation dryer for pre-drying, mechanically applying filtrate as mother liquor, wherein the temperature of flash evaporation pre-drying is 140 ℃, and the moisture of pre-drying is controlled to be less than or equal to 2%. (ii) a

4) Crushing and drying: crushing the pre-dried material, then conveying into a high-temperature horizontal dryer, and drying at 160 ℃ to obtain 743kg of product D₅₀0.51 μm, D₁₀₀2.87 microns, 0.07 percent of water and 307 ℃ of 0.5 percent of thermal weight loss temperature.

Example 2

1) Preparation of melamine cyanurate slurry: 370kg of melamine (with the purity of 99.5%) and 374kg of cyanuric acid (with the purity of 98.5%) are added into a 2000L horizontal reactor, mixed for 30 minutes, 10% wt of polyvinyl alcohol 0588 aqueous solution is added, the weight is 2kg, the mixture is stirred for 30 minutes, 100kg of deionized water (the conductivity is less than or equal to 5 mu s/cm) is added, and the mixture is stirred continuously for 40 minutes and mixed uniformly. Heating while stirring, and keeping at 80 ℃ for 1.5 hours to obtain a melamine cyanurate slurry primary product;

2) aqueous hydrothermal method: inputting the melamine cyanurate slurry obtained in the step 1) into a 5000L reaction kettle, adding 3000L mother liquor and deionized water (the balance is complemented by the deionized water), heating and stirring at the temperature of 95 ℃, discharging within 1 hour, and discharging with the viscosity of 120 cP;

3) filtering and pre-drying: filtering the materials by a centrifugal machine, inputting filter cakes into a flash evaporation dryer for pre-drying, mechanically applying filtrate as mother liquor, wherein the temperature of flash evaporation pre-drying is 140 ℃, and the moisture of pre-drying is controlled to be less than or equal to 2%. (ii) a

4) Crushing and drying: crushing the pre-dried material, then inputting into a high-temperature horizontal dryer, drying at 160 ℃ to obtain 742kg of product D₅₀0.48 μm, D₁₀₀2.66 μm, 0.07% water, and 309 ℃ of 0.5% thermal weight loss temperature.

Example 3

1) Preparation of melamine cyanurate slurry: 370kg of melamine (with the purity of 99.5%) and 374kg of cyanuric acid (with the purity of 98.5%) are added into a 2000L horizontal reactor, mixed for 30 minutes, added with 1kg of calcium pyrophosphate, stirred for 30 minutes, added with 100kg of deionized water (the conductivity is less than or equal to 5 mus/cm), stirred continuously for 40 minutes and mixed uniformly. Heating while stirring, and keeping at 80 ℃ for 1.5 hours to obtain a melamine cyanurate slurry primary product;

2) aqueous hydrothermal method: inputting the melamine cyanurate slurry obtained in the step 1) into a 5000L reaction kettle, adding 3000L mother liquor and deionized water (the balance is complemented by the deionized water), heating and stirring at the temperature of 95 ℃, discharging within 1 hour, and discharging with the viscosity of 125 cP;

3) filtering and pre-drying: filtering the materials by a centrifugal machine, inputting filter cakes into a flash evaporation dryer for pre-drying, mechanically applying filtrate as mother liquor, wherein the temperature of flash evaporation pre-drying is 140 ℃, and the moisture of pre-drying is controlled to be less than or equal to 2%. (ii) a

4) Crushing and drying: crushing the pre-dried material, then inputting the crushed material into a high-temperature horizontal dryer, drying the crushed material at 160 ℃,742.5kg of product, D, are obtained₅₀0.55 μm, D₁₀₀2.90 μm, 0.05% moisture, and a 0.5% thermal weight loss temperature of 310 ℃.

Example 4

1) Preparation of melamine cyanurate slurry: 370kg of melamine (with the purity of 99.5%) and 374kg of cyanuric acid (with the purity of 98.5%) are added into a 2000L horizontal reactor, mixed for 30 minutes, calcium pyrophosphate with the weight of 0.5kg is added, stirred for 30 minutes, 150kg of deionized water (the conductivity is less than or equal to 5 mus/cm) is added, and the mixture is stirred continuously for 40 minutes and mixed uniformly. Heating while stirring, and keeping at 80 ℃ for 2.0 hours to obtain a melamine cyanurate slurry primary product;

2) aqueous hydrothermal method: inputting the melamine cyanurate slurry obtained in the step 1) into a 5000L reaction kettle, adding 3000L mother liquor and deionized water (the balance is made up by deionized water), heating and stirring at the temperature of 90 ℃, discharging for 80 minutes, and the viscosity is 131 cP;

3) filtering and pre-drying: filtering the materials by a centrifugal machine, inputting filter cakes into a flash evaporation dryer for pre-drying, mechanically applying filtrate as mother liquor, wherein the temperature of flash evaporation pre-drying is 140 ℃, and the moisture of pre-drying is controlled to be less than or equal to 2%. (ii) a

4) Crushing and drying: crushing the pre-dried material, then inputting into a high-temperature horizontal dryer, and drying at 240 ℃ to obtain 742.5kg of product D₅₀0.41 μm, D₁₀₀2.70 μm, 0.02% water, and a 0.5% thermal weight loss temperature of 312 ℃.

Comparative example 1

1100 l of deionized water was placed in a 2000l reactor, 55kg of melamine and 55.5kg of cyanuric acid were added, the viscosity was about 9%, the mixture was heated with stirring for 1 hour to 90 ℃ and maintained at 90. + -. 5 ℃ for 2 hours, the viscosity was 653 cP. Filtering, drying and pulverizing to obtain 98kg of melamine cyanurate, D₅₀0.67 μm, D₁₀₀11.0 μm, 0.06% moisture, and a 0.5% thermal weight loss temperature of 305 ℃.

Comparative example 2:

185kg of melamine and 187kg of cyanuric acid are added into a 1000L horizontal reactor, the mixing time is 30 minutes, the mixture is stirred evenly, 50kg of deionized water (the conductivity is not more than 5 mu s/cm) is added,stirring is continued for 40 minutes and mixing is carried out uniformly. Then heated with stirring at 80 ℃ for 1.5 hours to obtain a melamine cyanurate aqueous slurry. Drying at 240 deg.C, pulverizing to obtain 372kg melamine cyanurate, D₅₀Is 3.8 μm, D₁₀₀23.6 μm, 0.06% water, and a 0.5% thermal weight loss temperature of 302 ℃.

The application example is that the spinning-grade halogen-free flame-retardant nylon is prepared on a double screw according to the following proportion.

According to parts by weight: 12 percent of melamine cyanurate, 0.5 percent of lubricant calcium stearate, 0.1 percent of antioxidant 1098, 0.05 percent of antioxidant 168, 87.35 percent of nylon 6M2400, the set temperature is 180 DEG and 250 ℃, and the screw rotating speed is 300 rpm.

TABLE 1 comparison of the properties of melamine cyanurate obtained according to the invention

The data in table 1 show that the MCA prepared by the present invention has no tailing in particle size and high thermal decomposition temperature.

Table 2, table for comparing performances of halogen-free flame-retardant nylon yarn prepared by the product of the invention

Flame retardant	LOI	UL94 vertical Combustion	Phenomenon of machining
				Is free of	26	V2，T1＝12s	Spinning: good and high strength
Comparative example 1	30	V2，T1＝6-8s	Spinning: poor continuity and slightly large smoke
				Comparative example 2	32	V2，T1＝4-5s	Spinning: poor continuity and slightly large smoke
Example 1	34	V2，T1＝2-3s	Spinning: good continuity and small smoke
				Example 2	36	V2，T1＝1-2s	Spinning: good continuity and small smoke
Example 3	34	V2，T1＝2-3s	Spinning: good continuity and small smoke
				Example 3	36	V2，T1＝0-2s	Spinning: good continuity and small smoke

The data in table 2 show that, compared with comparative examples 1-2, examples 1-4 have less particle size tailing, significantly improved blocking phenomenon in nylon spinning, and good continuity; the thermal decomposition temperature is high, the processing decomposition is less, and the smoke is less; the dispersion was good, the appearance of the spun yarn was as shown in fig. 2, the surface of example 1 was smooth and free of small protrusions, while the surface of comparative examples 1 and 2 had more protrusions as shown in fig. 3 and 4.

While the invention has been described with respect to a preferred embodiment, it will be understood by those skilled in the art that the foregoing and other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention. Those skilled in the art can make various changes, modifications and equivalent arrangements, which are equivalent to the embodiments of the present invention, without departing from the spirit and scope of the present invention, and which may be made by utilizing the techniques disclosed above; meanwhile, any changes, modifications and variations of the above-described embodiments, which are equivalent to those of the technical spirit of the present invention, are within the scope of the technical solution of the present invention.