A method for reducing the free melamine content in MCA products

Abstract

The present invention discloses a method for reducing the free melamine content in an MCA product. The method synthesizes MCA using an ultrasonic reaction synthesis method, molar ratio feeding, raw material wetting and dispersion, filter cake water washing, and mother liquor recycling method, thereby achieving the purpose of reducing the free melamine content in the MCA product to below 0.1%. The low-residue MCA product has good dispersibility in PA6.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant synthesis and relates to a method for reducing the content of free melamine in an MCA product. Background Art

[0002] Melamine cyanurate (MCA) is a multifunctional fine chemical developed in Japan in the early 1980s. Its molecular structure consists of a triazine ring complex formed by secondary bonds between melamine and cyanuric acid. It appears as a slippery white crystalline micropowder and is non-toxic, odorless, and poorly soluble in water and common organic solvents. MCA is a high-performance nitrogen-based halogen-free flame retardant that complies with the EU RoHS Directive and REACH regulations. It is widely used in halogen-free flame retardant applications in polymers such as polyamides, polyurethanes, and polyesters, offering the advantages of being halogen-free, low-toxic, and environmentally friendly.

[0003] The European Chemicals Agency (ECHA) updated its SVHC list on January 17, 2023, adding melamine (CAS 108-78-1) to the Candidate List of Substances of Very High Concern (SVHC). Inclusion on the SVHC Candidate List carries corresponding obligations, including the obligation for manufacturers to ensure that the melamine concentration in articles does not exceed 0.1%. Consequently, the melamine content requirement in articles has been lowered from the previous 0.3% to 0.1%.

[0004] Furthermore, excessive melamine content in the product can reduce the main content and thermal stability of the MCA product, further impacting its performance in downstream substrate applications. Firstly, this can affect MCA's compatibility with polymers, leading to poor dispersion in the substrate and the formation of white spots on the surface of the finished product. Secondly, it can reduce MCA's flame retardancy. Therefore, reducing the free melamine content in MCA products is crucial. Summary of the Invention

[0005] To address the above issues, the present invention provides a method for reducing the free melamine content in MCA products. This method utilizes ultrasonic reaction synthesis, molar ratio feeding, raw material wetting and dispersion, filter cake washing, and mother liquor recycling to synthesize MCA. This method achieves the goal of reducing the free melamine content in the MCA product to below 0.1%. The low-residue MCA product exhibits excellent dispersibility in PA6.

[0006] The technical solution of the present invention is as follows: A method for reducing the free melamine content in MCA products, characterized in that:

[0007] 1) Taking MCA mother liquor and testing the content of free melamine and free cyanuric acid therein; Based on the mother liquor test results, the feeding amounts of melamine and cyanuric acid are calculated according to a 1:1 molar ratio;

[0008] 2) Add melamine and cyanuric acid to the MCA mother liquor and beat it for full wetting and dispersion;

[0009] 3) After wetting and dispersion are completed, all the raw material slurry is added to the ultrasonic reactor and ultrasonically reacted at 95-98°C for 10-30 minutes;

[0010] 4) After the reaction is completed, the reaction solution is filtered, and the filter cake is washed with water, dried, and crushed to obtain the MCA product.

[0011] The ultrasonic reactor is a sound wave with a frequency higher than 20 kHz. It utilizes ultrasound to enhance the reactivity of the system and promote rapid chemical reactions. It also utilizes the secondary effects of ultrasound, mechanical oscillation, and diffusion, to accelerate the full mixing of reactants. The ultrasonic parameters include the ultrasonic time, ultrasonic interval time, and total ultrasonic time. Optimally, the ultrasonic time is 10 seconds, the ultrasonic interval time is 10 seconds, and the total ultrasonic time is 20 minutes.

[0012] The wetting and dispersing treatment temperature is room temperature, and the wetting and dispersing beating time is 10-30 minutes.

[0013] Furthermore, the MCA mother liquor is the filtrate produced by filtration and water washing during the MCA preparation process, and the filtrate is recycled without the need for wastewater treatment.

[0014] The principle of the present invention is that MCA is formed by the chemical reaction of melamine and cyanuric acid molecules. Only when the reactants are evenly mixed and fully reacted can the raw materials be fully utilized, thereby reducing the free raw materials in the product. The raw materials are treated with a wetting dispersion process to reduce their surface tension on the one hand and increase their dispersion properties in the aqueous system on the other hand, thereby increasing the contact area between the raw materials. The ultrasonic reactor utilizes the "cavitation" effect of ultrasound to enhance the reactivity of the system, generating instantaneous high temperature and high pressure sufficient to trigger a chemical reaction, forming a local high-energy center to promote the rapid and efficient progress of the chemical reaction. At the same time, the mechanical oscillation and diffusion effects of the ultrasonic secondary effect accelerate the full mixing and collision of free reactants. Therefore, the use of ultrasonic reaction not only accelerates the mixing of reactants, but also promotes the rapid and efficient completion of chemical reactions.

[0015] The technical effects of the present invention are as follows: first, the raw materials are subjected to a wetting and dispersion treatment to reduce the surface tension of the materials and improve the diffusion performance of the materials in the aqueous phase system; second, an ultrasonic reactor is used as the reaction equipment, which not only accelerates the mixing of the reactants, but also promotes the rapid and efficient completion of the chemical reaction and the full reaction; third, the feed ratio is fed and synthesized according to a molar ratio of 1:1 to ensure that the raw materials are fully utilized and the reaction is sufficient; fourth, the filter cake is further purified by washing with water; the above method reduces the free melamine content in the MCA product to below 0.1%. In addition, the filtrate generated during the reaction process is recycled, and there is no need for wastewater treatment, thus achieving energy-saving and environmentally friendly production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 TG spectrum of melamine cyanurate prepared in Example 1;

[0017] Figure 2 This is a diagram showing the dispersion effect of melamine cyanurate prepared in Example 1 in a PA6 substrate. DETAILED DESCRIPTION

[0018] The effects are described below with reference to the examples and accompanying drawings. The MCA mother liquor used in this example is the filtrate produced by filter pressing and water washing during the MCA preparation process.

[0019] Example 1:

[0020] 1. Weigh 300 parts by weight of MCA mother liquor and detect the free melamine and free cyanuric acid in the mother liquor; according to the test results, the free melamine is 0.0148% and the free cyanuric acid is 0.0079%; according to the molar ratio of 1:1, the melamine feeding amount is calculated to be 17.80 parts by weight and the cyanuric acid feeding amount is 18.22 parts by weight;

[0021] 2. Add the MCA mother liquor into the beating tank, add the raw materials melamine and cyanuric acid, stir and beat for 15 minutes at room temperature for wet dispersion treatment;

[0022] 3. After wetting and dispersion treatment, the raw material slurry was added to the ultrasonic reactor, mechanical stirring was turned on, heating was turned on, ultrasound was turned on and the ultrasound parameters were set (ultrasonic time 10s, ultrasonic interval time 10s, total ultrasonic time 20min), and the reaction was carried out at 98°C for 0.5h;

[0023] 4. After the reaction is completed, the reaction solution is filtered, 300 parts by weight of 75°C water is added to wash the filter cake, the filter cake is dried and crushed to obtain an MCA product with a main content of 99.67%, 0.0860% free melamine, 0.0940% free cyanuric acid, and a 1% thermal weight loss temperature of 362.92°C.

[0024] Figure 1 Shown is the TG spectrum of MCA prepared in this example, Figure 1 It can be seen that the product has low free melamine content and high temperature resistance.

[0025] Example 2:

[0026] 1. Weigh 300 parts by weight of MCA mother liquor and detect the free melamine and free cyanuric acid in the mother liquor; based on the test results, the free melamine content is 0.1767% and the free cyanuric acid content is 0.0162%; the melamine feed amount is calculated to be 17.80 parts by weight and the cyanuric acid feed amount is 18.69 parts by weight based on a molar ratio of 1:1;

[0027] 2. Add the MCA mother liquor into the beating tank, add the raw materials melamine and cyanuric acid, stir and beat for 15 minutes at room temperature for wet dispersion treatment;

[0028] 3. After wetting and dispersion treatment, the raw material slurry was added to the ultrasonic reactor; mechanical stirring was turned on, heating was turned on, ultrasound was turned on and the ultrasonic parameters were set (ultrasonic time 10s, ultrasonic interval time 10s, ultrasonic total time 10min), and the reaction was carried out at 98°C for 0.5h;

[0029] 4. After the reaction is completed, the reaction solution is filtered, and 300 parts by weight of 75°C water is added to wash the filter cake. The filter cake is dried and crushed to obtain an MCA product with a main content of 99.58%, 0.0691% free melamine, 0.1522% free cyanuric acid, and a 1% thermal weight loss temperature of 352.59°C.

[0030] Example 3:

[0031] 1. Weigh 300 parts by weight of MCA mother liquor and detect the free melamine and free cyanuric acid in the mother liquor; based on the test results, the free melamine is 0.0710% and the free cyanuric acid is 0.1445%. According to the molar ratio of 1:1, the melamine feeding amount is calculated to be 18.01 parts and the cyanuric acid feeding amount is 18.20 parts;

[0032] 2. Add the MCA mother liquor into the beating tank, add the raw materials melamine and cyanuric acid, stir and beat for 15 minutes at room temperature for wet dispersion treatment;

[0033] 3. After wetting and dispersion treatment, the raw material slurry was added to the ultrasonic reactor; mechanical stirring was turned on, heating was turned on, ultrasound was turned on and the ultrasonic parameters were set (ultrasonic time 10s, ultrasonic interval time 10s, ultrasonic total time 10min), and the reaction was carried out at 98°C for 0.5h;

[0034] 4. After the reaction is completed, the reaction solution is filtered, and 300 parts by weight of 75°C water is added to wash the filter cake. The filter cake is dried and crushed to obtain an MCA product with a main content of 99.54%, free melamine 0.0951%, free cyanuric acid 0.1024%, and a 1% thermal weight loss temperature of 357.81°C.

[0035] Comparative Example 1:

[0036] 1. Weigh 300 parts by weight of MCA mother liquor, containing 0.1767% free melamine and 0.0162% free cyanuric acid; adjust the feeding amount of melamine to 18.0 parts by weight and cyanuric acid to 18.0 parts by weight in a mass ratio of 1:1;

[0037] 2. Add the MCA mother liquor into the beating tank, add the raw materials melamine and cyanuric acid, stir and beat for 15 minutes at room temperature for wet dispersion treatment;

[0038] 3. After wetting and dispersion treatment, the raw material slurry was added to the ultrasonic reactor; mechanical stirring was turned on, heating was turned on, ultrasound was turned on and the ultrasonic parameters were set (ultrasonic time 10s, ultrasonic interval time 10s, ultrasonic total time 10min), and the reaction was carried out at 98°C for 0.5h;

[0039] 4. After the reaction is completed, the reaction solution is filtered, and 300 parts by weight of 75°C water is added to wash the filter cake. The filter cake is dried and crushed to obtain an MCA product with a main content of 99.29%, 0.2353% free melamine, 0.1030% free cyanuric acid, and a 1% thermal weight loss temperature of 336.89°C.

[0040] Comparative Example 2:

[0041] 1. Weigh 300 parts by weight of MCA mother liquor and detect the free melamine and free cyanuric acid in the mother liquor; based on the test results, the free melamine is 0.0148% and the free cyanuric acid is 0.0079%. According to the molar ratio of 1:1, the melamine feeding amount is calculated to be 17.80 parts by weight and the cyanuric acid feeding amount is 18.22 parts by weight;

[0042] 2. Take the MCA mother liquor and add it into the beating tank, add the raw materials melamine and cyanuric acid, stir and beat for 15 minutes at room temperature for wet dispersion treatment;

[0043] 3. After wetting and dispersion treatment, the raw material slurry was added to the ultrasonic reactor; mechanical stirring was turned on, heating was turned on, ultrasound was turned on and the ultrasonic parameters were set (no ultrasonic interval was set, continuous ultrasound was used, and the total ultrasonic time was 20 minutes), and the reaction was carried out at 98°C for 0.5 hours;

[0044] 4. After the reaction is completed, the reaction solution is filtered, and 300 parts by weight of 75°C water is added to wash the filter cake. The filter cake is dried and crushed to obtain an MCA product with a main content of 99.30%, free melamine 0.2156%, free cyanuric acid 0.1905%, and a 1% thermal weight loss temperature of 337.51°C.

[0045] Comparative Example 3:

[0046] 1. Weigh 300 parts by weight of MCA mother liquor and detect the free melamine and free cyanuric acid in the mother liquor; based on the test results, the free melamine is 0.0148% and the free cyanuric acid is 0.0079%. According to the molar ratio of 1:1, the melamine feeding amount is calculated to be 17.80 parts by weight and the cyanuric acid feeding amount is 18.22 parts by weight;

[0047] 2. Take the MCA mother liquor and add it into the beating tank, add the raw materials melamine and cyanuric acid, stir and beat for 15 minutes at room temperature for wet dispersion treatment;

[0048] 3. After wetting and dispersion treatment, the raw material slurry was added to the ultrasonic reactor; mechanical stirring was started, heating was started, ultrasound was started and the ultrasound parameters were set (ultrasonic time 10s, ultrasonic interval time 60s, total ultrasonic time 20min), and the reaction was carried out at 98°C for 0.5h;

[0049] 4. After the reaction is completed, the reaction solution is filtered, and 300 parts by weight of 75°C water is added to wash the filter cake. The filter cake is dried and crushed to obtain an MCA product with a main content of 99.43%, free melamine 0.1265%, free cyanuric acid 0.1186%, and a 1% thermal weight loss temperature of 347.92°C.

[0050] Comparative Example 4:

[0051] 1. Weigh 300 parts by weight of MCA mother liquor and detect the free melamine and free cyanuric acid in the mother liquor; based on the test results, the free melamine is 0.0148% and the free cyanuric acid is 0.0079%. According to the molar ratio of 1:1, the melamine feeding amount is calculated to be 17.80 parts by weight and the cyanuric acid feeding amount is 18.22 parts by weight;

[0052] 2. Take the MCA mother liquor and add it into the beating tank, add the raw materials melamine and cyanuric acid, stir and beat for 15 minutes at room temperature for wet dispersion treatment;

[0053] 3. After wetting and dispersion treatment, the raw material slurry was added to the reactor; mechanical stirring was started, heating was started, ultrasound was started and the ultrasound parameters were set (ultrasound time 10s, ultrasound interval time 10s, total ultrasound time 30min), and the reaction was carried out at 98°C for 0.5h;

[0054] 4. After the reaction is completed, the reaction solution is filtered, and 300 parts by weight of 75°C water is added to wash the filter cake. The filter cake is dried and crushed to obtain an MCA product with a main content of 99.54%, free melamine 0.0921%, free cyanuric acid 0.1053%, and a 1% thermal weight loss temperature of 359.64°C.

[0055] The product index test results obtained in the above examples are shown in Table 1.

[0056] Table 1 Product index test results

[0057]

[0058] Application examples:

[0059] The MCA products described in Example 1 and Comparative Examples 1-2 were used in PA6 materials for application evaluation experiments according to the formulation in Table 2. The specific experimental steps were as follows: 1) The PA6 raw material was dried in a drying oven at 100°C for 3 hours and cooled for later use. 2) MCA, PA6 raw material, and carbon black were weighed according to the experimental formulation and added to a sample bag and manually mixed. 3) The twin-screw 30 extruder was set to a high temperature (Zone 1: 225°C; Zone 2: 227°C; Zone 3: 230°C; Zone 4: 235°C; Zone 5: 235°C; Zone 6: 230°C; Zone 7: 227°C; Zone 8: 225°C). Once the temperatures reached the set temperature, the oil pump, main engine, and feeder were sequentially started. The mixed materials were added, extruded, stretched, and pelletized to obtain application experimental samples. 4) The extruded strips were observed and recorded throughout the experiment. 5) After the experiment was completed, the equipment was cleaned and shut down. 6) The extruded pellets were dried at 100°C for 5 hours and cooled for later use. 7) Set the injection molding machine to a high temperature (stage 1: 225°C; stage 2: 230°C; stage 3: 225°C). Once the temperature reaches the set point, start the motor and set the injection pressure (shot 1: 23 MPa, shot 2: 21 MPa, shot 3: 17 MPa, shot 4: 15 MPa). Molded the flame-retardant sample. 8) Use a vertical flame tester to test the flame retardancy. See Table 3 for specific application results.

[0060] Table 2 Application test formula

[0061] Recipe Ingredients Addition ratio (wt%) PA6 87.7 MCA 12.0 carbon black 0.3

[0062] Table 3 Application effect comparison table

[0063] serial number Spline Appearance Flame retardant UL-94 Example 1 No white spots on the surface or inside of the spline 10 / 10V-0 Comparative Example 1 There are many white spots on the surface and inside of the spline 3 / 10V-0 Comparative Example 2 There are many white spots on the surface and inside of the spline 4 / 10V-0

[0064] The dispersion effect of MCA prepared in Example 1 of the present invention in PA6 is shown in detail. Figure 2 , indicating that the prepared low-residue MCA product has good dispersibility in PA6 and no white powder precipitation is observed.

[0065] Table 3 shows that the low-residue melamine cyanurate prepared in Example 1 of the present invention exhibits excellent dispersibility and flame retardancy. In Comparative Example 1, the materials were not synthesized according to the molar ratio, which prevented the reaction from proceeding fully, resulting in a high residue in the product and poor application performance. In Comparative Example 2, ultrasound was not paused, and ultrasound was continuously applied throughout the reaction, affecting the MCA synthesis process (dissolution-deposition-dissolution-redeposition). This continuous ultrasound operation inhibited MCA deposition, ultimately resulting in a low melamine cyanurate content and high residue in the synthesized product. Consequently, the product exhibited poor dispersibility and flame retardancy.

Claims

1. A method for reducing the free melamine content in an MCA product, characterized in that: 1) taking an MCA mother liquor and detecting the content of free melamine and free cyanuric acid therein; and calculating and determining the amount of melamine and cyanuric acid to be fed according to a molar ratio of 1:1 based on the test results of the MCA mother liquor; 2) Add melamine and cyanuric acid to the MCA mother liquor and beat it for full wetting and dispersion; 3) After wetting and dispersion are completed, all the raw material slurry is added to an ultrasonic reactor and ultrasonically reacted at 95-98°C; the ultrasonic reactor uses sound waves with a frequency higher than 20 kHz, and the ultrasonic reaction is specifically: ultrasonic time 10 seconds, ultrasonic interval time 10 seconds, and total ultrasonic time 10-20 minutes; 4) After the reaction is completed, the reaction solution is filtered, and the filter cake is washed with water, dried, and crushed to obtain the MCA product.

2. The method for reducing the free melamine content in an MCA product according to claim 1, wherein: The wetting and dispersing treatment temperature is room temperature.

3. A method for reducing the free melamine content in an MCA product as claimed in claim 2, characterized in that: The beating time for the wetting and dispersing is 10-30 minutes.

4. A method for reducing the free melamine content in an MCA product according to any one of claims 1 to 3, characterized in that: The MCA mother liquor is the filtrate produced by filtration and water washing during the MCA preparation process, and the filtrate is recycled.

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