CN114751869B

CN114751869B - Preparation method of high-dispersion melamine cyanurate flame retardant

Info

Publication number: CN114751869B
Application number: CN202210421251.1A
Authority: CN
Inventors: 刘婷; 徐有敏; 索伟; 宋传君; 王艳辉; 徐亮; 段金凤; 王鲁静; 常玉宝; 乔志川
Original assignee: Shandong Taixing New Materials Co ltd
Current assignee: Shandong Taixing New Materials Co ltd
Priority date: 2022-04-21
Filing date: 2022-04-21
Publication date: 2024-02-13
Anticipated expiration: 2042-04-21
Also published as: CN114751869A

Abstract

The invention discloses a preparation method of a high-dispersion melamine cyanurate flame retardant. The method comprises the steps of firstly preparing suspension by grinding mixed liquid of melamine/cyanuric acid and water to control raw material activity, and then preparing the high-dispersion melamine cyanurate flame retardant by adopting a liquid-liquid feeding and sectional synthesis method. The reaction process of the invention does not introduce other substances, the reaction mother liquor is recycled, green and environment-friendly production is realized, the reaction is carried out under normal pressure, safe and low-cost production is realized, and the invention is suitable for industrial production.

Description

Preparation method of high-dispersion melamine cyanurate flame retardant

Technical Field

The invention relates to a preparation method of a high-dispersion melamine cyanurate flame retardant, and belongs to the technical field of flame retardants.

Background

Melamine Cyanurate (MCA) is a nitrogen flame retardant with high nitrogen content, good flame retardant effect, low toxicity and low smoke. The polyurethane is widely applied to polyamide, rubber, polyurethane, epoxy resin, polypropylene and other materials. When the polyamide foam flame-retardant by the product burns, the formed carbon foam layer plays a role in protecting the polymer and insulating heat from oxygen. With the addition of the product, the smoke density and toxic gas of the polymer can be greatly reduced, and meanwhile, no irritant hydrogen halide gas is generated.

MCA is formed by the hydrogen bonding of melamine and cyanuric acid molecules. At present, the preparation method of the MCA mainly comprises the following three steps:

1. high temperature melting process

Directly carrying out melt reaction on melamine and cyanuric acid at 300 ℃. The method has simple process and short flow, but the raw materials are lost during the reaction, the yield is low, and the high temperature of the reaction has high requirements on equipment.

2. Urea process

Mixing a certain amount of urea, a dispersing agent and melamine, adding the mixture into a container provided with a stirrer and a reflux condenser, and performing solid phase reaction at 280-300 ℃ for 60-70min to obtain a crude MCA product, and refining the crude MCA product after hydrolysis.

3. Solution process

The solution method is the main stream method for industrial production, melamine and cyanuric acid are used as raw materials, water is used as solvent to prepare suspension, and MCA products are prepared by heating reaction. The method has simple process, but the system has low solid content and high drying energy consumption. To increase the solid content of the reaction system, it can be prepared by adjusting the pH of the reaction mixture by adding acidic and basic reagents thereto or by adding a modifier.

Currently, the patent/literature discloses a number of methods for preparing MCA: EP 5507677A1 adopts inorganic acid, reduces the water/reactant ratio and improves the production efficiency under the condition that the pH value is less than or equal to 1. Yang Xionglin A process for preparing MCA by reaction of melamine and cyanuric acid in water with sodium carbonate to adjust the pH of the reaction system to 8-8.5 at 90-95℃is provided (Yang Xionglin. Melamine cyanurate and its use [ J ]. Modern chemical 1991, (04), 51). CN 1506356A discloses that melamine cyanurate products with the grain diameter of 5-55 mu m can be prepared by taking melamine and cyanuric acid as raw materials, adopting an ammonia water solution with the concentration of 2-14% as a solvent, and reacting at the temperature of 100-200 ℃ and the pressure of 0.05-1.5 MPa. Patent CN 101914220B discloses a preparation method of nano melamine cyanurate, which uses a mixed solution of water and an organic solvent as a reaction medium, and treats the surface of MCA through a silane coupling agent or stearic acid, thereby preparing nano MCA. Patent CN 102093300A discloses a preparation method of high-fluidity high-purity crystalline flake melamine cyanurate, which comprises the steps of press-filtering melamine and cyanuric acid reaction mixed liquid, mixing a filter cake with silicone oil to obtain a semi-finished product, drying the semi-finished product, and curing and crystallizing in vacuum to obtain an MCA product.

The method for preparing the MCA disclosed in the above patent/literature has the defects of different degrees, such as acid, alkali and modifier introduced in the reaction process, corrosion to equipment to a certain extent, and increase of production wastewater treatment cost, and high requirements on equipment and high cost due to reaction conditions such as pressurization, vacuum and the like. Meanwhile, the prepared large-particle-size MCA has larger particle size and has great influence on the mechanical property of the high polymer material, while the nanometer MCA has undersize and large specific surface area, and the powder is easy to agglomerate in the application process, so that the dispersion is uneven.

Disclosure of Invention

Aiming at the problems, the invention provides a preparation method of a high-dispersion melamine cyanurate flame retardant. The method comprises the steps of firstly preparing suspension by grinding mixed liquid of melamine/cyanuric acid and water to control raw material activity, and then preparing the high-dispersion melamine cyanurate flame retardant by adopting a liquid-liquid feeding and sectional synthesis method. The reaction process of the invention does not introduce other substances, the reaction mother liquor is recycled, green and environment-friendly production is realized, the reaction is carried out under normal pressure, safe and low-cost production is realized, and the invention is suitable for industrial production.

The technical scheme of the invention is as follows: a preparation method of a high-dispersion melamine cyanurate flame retardant is characterized in that,

1) Adding the mixed solution of melamine and water into a sand mill for grinding to prepare melamine suspension;

2) Adding the mixed solution of cyanuric acid and water into a sand mill for grinding to prepare cyanuric acid suspension;

3) Adding melamine suspension into a reactor at one time, adding most of cyanuric acid suspension into the reactor, and reacting for 0.5-1h at the temperature of 95-98 ℃ under normal pressure; then adding the rest cyanuric acid suspension, and continuously reacting for 0.5-1h at the temperature of 95-98 ℃ under normal pressure; and drying after the reaction is finished to obtain a melamine cyanurate product.

Preferably, the sand mill is a horizontal sand mill, and the grinding medium of the sand mill is zirconia beads with the size of 0.8-1.2 mu m. The grinding of the raw materials is to improve the reactivity of the raw materials, increase the reactive sites of the raw materials, increase the effective collision probability of reactants, accelerate the reaction rate and shorten the reaction time.

Preferably, the melamine in the melamine suspension has a particle size in the range of 8-10 μm. The cyanuric acid particle size in the cyanuric acid suspension is 10-12 μm. Particle size distribution requirements: melamine suspension D ₉₈ Cyanuric acid suspension D less than or equal to 30 mu m ₉₈ ≤40μm。

Preferably, the molar ratio of cyanuric acid to melamine is from 1:1 to 1.02.

Preferably, the amount of water used in said steps 1) and 2) is 1.5-3 and 1-2.5 times, preferably 2-2.5 times and 1.5-2 times, respectively, the mass of cyanuric acid and melamine.

Preferably, the volume ratio of the cyanuric acid suspension to the two feeds is 2:0.8-1.2. The melamine suspension is added at one time, and the cyanuric acid suspension is added twice, so that the partial alkali environment of the reaction system is kept, and the partial alkali environment can inhibit the longitudinal growth of melamine cyanurate, so that the flaky high-dispersion product is prepared.

The principle of the invention is as follows: MCA is formed by the hydrogen bonding of melamine and cyanuric acid molecules. The hydrogen bond is usually formed by a substance in a liquid state, and raw materials are ground to prepare a suspension, so that the raw materials react in the suspension state to promote the formation of the hydrogen bond. Meanwhile, the intermolecular hydrogen bonding rate depends on intermolecular active sites, the active sites are more, the effective intermolecular collision probability is high, the intermolecular hydrogen bonding is easy to generate, and the reaction rate is improved. However, the suspension cannot be ground without limitation, and the particle size of the suspension must be controlled within a certain range. If the particle size of the suspension is too large, the specific surface area of the reactants is small, the reactive sites are few, the effective collision probability among the reactants is small, the reaction time is prolonged, and the reaction efficiency is low. If the particle size of the suspension is too small, grinding time is needed, energy consumption is increased, meanwhile, the particle size is too small, the viscosity of a suspension system is increased, the material transferring difficulty is caused by too high viscosity, the stirring pressure is high, and then the mixing uniformity of materials and the quality of products are influenced. Therefore, control of the raw material suspension particle size range is critical.

The invention has the technical effects that: firstly, grinding raw materials to improve the reactivity of the raw materials and obtain a high-purity MCA product; secondly, the raw materials are fully mixed in a liquid-liquid feeding mode, so that the uniformity of a reaction mixture is ensured, and the reaction is full; thirdly, raw material feeding is controlled, melamine is added at one time, cyanuric acid is added in two times, and a reaction system is controlled to be maintained in a partial alkali environment, so that a high-dispersion MCA product is easy to obtain. By adopting the preparation method, other substances are not introduced in the reaction process, the reaction mother liquor is recycled, the green environment-friendly production is realized, the reaction is carried out under the normal pressure condition, and the safe and low-cost production is realized.

Drawings

FIG. 1 is an SEM image of highly dispersed melamine cyanurate prepared in example 1;

fig. 2 is an SEM image of the application of the highly dispersed melamine cyanurate prepared in example 1 in TPU.

Detailed Description

The effects thereof are further described below with reference to the examples and drawings. Particle size analyzer model: BT-9300S laser particle size distribution apparatus.

The granularity detection method comprises the following steps: 1) Weighing 0.5g of sample, adding into a beaker, and weighing 60ml of water into the beaker; 2) Placing the beaker into an ultrasonic cell disruption instrument for ultrasonic dispersion for 3min; 3) Opening a switch of the particle size analyzer, opening circulation, and cleaning a sample cell of the particle size analyzer for 3 times; 4) Setting test parameters, opening an ultrasonic button, sucking the solution after ultrasonic dispersion by using a rubber head dropper, adding the solution into a sample cell of a particle size analyzer, controlling the sample adding concentration, and keeping the shading degree range from 6 to 8; 5) After the shading degree is stable, clicking to start testing, 6) finishing the testing, storing data, and cleaning the particle sizer.

Example 1:

1) Adding 600g of melamine and 1428g of water into a sand mill for grinding (zirconium oxide beads with the size of 1 mu m are taken as grinding media, the addition amount of the ground substances is not more than 2/3 of the volume of a cylinder of the sand mill, and the same applies below), and preparing melamine suspension with the average particle size of 9.3 mu m for later use;

2) Adding 614g cyanuric acid and 1000g water into a sand mill (same as above) for grinding, and preparing cyanuric acid suspension with average particle diameter of 11.5 μm for later use;

3) 2028g of melamine suspension is added into the reactor at one time, 1065g of cyanuric acid suspension is added, stirring and heating are started, the temperature reaches 98 ℃, the reaction is carried out for 0.5h at a constant temperature, 549g of cyanuric acid suspension is added, and the reaction is carried out for 0.5h at a constant temperature of 98 ℃. After the completion of the reaction, the mixture was dried (drying temperature: 110 ℃ C.) to obtain a flaky highly dispersed MCA product having a major content of 99.82% and an average particle diameter of 2.43. Mu.m.

SEM images of the high dispersion sheet MCA prepared in example 1 are shown in fig. 1, and it can be seen from fig. 1: the prepared MCA crystal has a flaky structure with the thickness of about 0.3 μm and the width of about 2 μm.

Example 2:

1) Adding 600g of melamine and 1428g of water into a sand mill for grinding, and preparing melamine suspension with the average particle size of 14.7 mu m for later use;

2) Adding a mixed solution of 614g of cyanuric acid and 1000g of water into a sand mill for grinding, and preparing cyanuric acid suspension with the average particle size of 17.3 mu m for later use;

3) 2028g of melamine suspension is added into a reactor at one time, 1065g of cyanuric acid suspension is added, stirring and heating are started, the temperature reaches 98 ℃, the reaction is carried out for 1h at a constant temperature, 549g of cyanuric acid suspension is added, and the reaction is carried out for 1h at a constant temperature of 98 ℃. The reaction was completed and dried to give an MCA product having a major content of 99.36% and an average particle size of 3.76. Mu.m.

Example 3:

1) Adding 600g of melamine and 1428g of water into a sand mill for grinding, and preparing melamine suspension with the particle size of 8.9 mu m for later use;

2) Adding 643g cyanuric acid and 1000g water into a sand mill for grinding, and preparing cyanuric acid suspension with the particle size of 10.4 mu m for later use;

3) 2028g of melamine suspension is added into a reactor at one time, 1075g of cyanuric acid suspension is added, stirring and heating are started, the temperature reaches 98 ℃, the reaction is carried out for 1h at a temperature, then 559g of cyanuric acid suspension is added, and the reaction is carried out for 1h at 98 ℃. After the completion of the reaction, the mixture was dried to obtain an MCA product having a main content of 99.03% and an average particle diameter of 3.28. Mu.m.

Example 4:

1) Adding 600g of melamine and 1428g of water into a sand mill for grinding, and preparing melamine suspension with the particle size of 9.7 mu m for later use;

2) Adding 614g cyanuric acid and 1000g water into a sand mill for grinding, and preparing cyanuric acid suspension with the particle size of 10.9 mu m for later use;

3) 2028g of melamine suspension is added into a reactor at one time, 1265g of cyanuric acid suspension is added, stirring and heating are started, the temperature reaches 98 ℃, the reaction is carried out for 1h at a temperature, 349g of cyanuric acid suspension is added, and the reaction is carried out for 0.5h at the temperature of 98 ℃. The reaction was completed and dried to obtain an MCA product having a major content of 99.32% and an average particle size of 2.95. Mu.m.

The product detection index and detection result of examples 1 to 4 are shown in Table 1.

Table 1: product detection index and detection result of examples 1 to 4

Application example 1:

the MCA products of examples 1-4 above were subjected to dispersion evaluation experiments in TPU materials according to the formulation of table 2. The specific test steps are as follows: 1) Drying TPU raw materials in a drying oven at 75 ℃ for 3 hours, and cooling for standby; 2) Weighing MCA, TPU raw materials and carbon black according to an experimental formula, adding the raw materials into a sample bag, and manually mixing the raw materials and the carbon black uniformly; 3) The twin screw 30 extruder set temperature was raised (one zone: 160 ℃; two areas: 163 ℃. Three regions: 166 deg.c; four regions: 170 ℃; five regions: 170 ℃; six areas: 166 deg.c; seven areas: 163 ℃. Eight areas: 160 ℃ and the temperature reaches the set temperature, sequentially starting an oil pump, a main engine and feeding, adding uniformly mixed materials, extruding, bracing and granulating to obtain an application experiment sample; 4) Observing and recording extrusion current, material blanking condition and extrusion spline and granule state in the experimental process; 5) After the experiment is finished, the equipment is cleaned and shut down. The specific application effects are shown in Table 3.

Table 2 application test recipe

Formulation ingredients	Addition ratio (wt%)
		TPU	87.7
MCA	12.0
		Carbon black	0.3

Table 3 application effect comparison table

Numbering device	Extrusion current, A	Discharging condition during production	Spline appearance
				Example 1	15.8	Quick blanking without bridging	Smooth surface and section without powder point
Example 2	15.0	Difficult blanking and bridging	The surface and the section have a small amount of white spots
				Example 3	14.6	Difficult to discharge and serious bridging	Rough surface and a large number of powder points
Example 4	15.5	Quick blanking without bridging	Smooth surface and 2-3 powder points on the tangent plane

The SEM image of the dispersion effect of the MCA prepared in example 1 of the present invention in TPU is shown in detail in fig. 2, and the surface-prepared sheet-like MCA product has good dispersibility in TPU.

As can be seen from table 3: the flaky melamine cyanurate prepared in the embodiment 1 of the invention has very good fluidity, the blanking is fast without bridging in the extrusion process, meanwhile, TPU sample strips obtained by extrusion are smooth in surface and free of powder points, and MCA products are well dispersed when being applied to TPU base materials. In example 2, the two raw material suspensions had too large particle diameters, resulting in low reactivity, and the agglomeration was severe, resulting in too large particle diameters and poor dispersibility. In example 3, the cyanuric acid is excessive, in example 4, the partial alkaline environment of the system is destroyed under two conditions, and the flaky high-dispersion MCA product with qualified main content can not be obtained, and the synthesized product is easy to agglomerate and has poor dispersibility.

Claims

1. The preparation method of the high-dispersion melamine cyanurate flame retardant is characterized by comprising the following steps of:

1) Adding the mixed solution of melamine and water into a sand mill for grinding to prepare melamine suspension; the particle size range of melamine in the melamine suspension is 8-10 mu m;

2) Adding the mixed solution of cyanuric acid and water into a sand mill for grinding to prepare cyanuric acid suspension; the grain diameter of cyanuric acid in the cyanuric acid suspension is 10-12 mu m;

3) Adding melamine suspension into a reactor at one time, adding most of cyanuric acid suspension into the reactor, and reacting for 0.5-1h at the temperature of 95-98 ℃ under normal pressure; then adding the rest cyanuric acid suspension, and continuously reacting for 0.5-1h at the temperature of 95-98 ℃ under normal pressure; drying after the reaction is finished to obtain a melamine cyanurate product; the molar ratio of cyanuric acid to melamine is 1:1-1.02; the volume ratio of the cyanuric acid suspension to the two feeds is 2:0.8-1.2.

2. The method for preparing the high-dispersion melamine cyanurate flame retardant according to claim 1, wherein the sand mill is a horizontal sand mill, and the grinding medium of the sand mill is zirconia beads with the size of 0.8-1.2 μm.

3. The method for preparing a highly dispersed melamine cyanurate flame retardant according to claim 1, wherein the water used in the steps 1) and 2) is 1.5 to 3 times and 1 to 2.5 times the mass of cyanuric acid and melamine, respectively.

4. A method for preparing a highly dispersed melamine cyanurate flame retardant according to claim 3, wherein the water used in steps 1) and 2) is 2-2.5 times and 1.5-2 times the mass of cyanuric acid and melamine, respectively.