CN116874701A - Preparation method of reactive melamine resin - Google Patents

Abstract

The invention relates to a preparation method of reactive melamine resin, which comprises the following steps of adding melamine, paraformaldehyde, methanol and polyalcohol into a reaction kettle according to a molar ratio of 1:4-6:2-4:2-4 to form a material I; heating under stirring, and when the temperature of the materials in the reaction kettle is 50-75 ℃, regulating the pH of the system to 9-11 and the reaction time to 2-3 h to obtain a material II; diethyl phosphite is added in a dropwise manner under normal pressure for 10-60 min, wherein the diethyl phosphite is 1-3.5 times of the mole number of melamine, and a material III is obtained; reacting the material III at 50-75 ℃ for 2-4 hours, and then adjusting the pH value to 7-8 to obtain a material IV; and (3) carrying out reduced pressure distillation on the material IV to separate out micromolecule substances in the system, wherein the reduced pressure distillation temperature is 70-100 ℃, the pressure is-0.08 to-0.10 MPa, and the moisture test is less than 0.5% by a gauge pressure meter to obtain the reactive melamine resin.

Description

Preparation method of reactive melamine resin

Technical field

The invention relates to a preparation method of reactive melamine resin.

Background technique

Polyurethane rigid foam (PUR) is an excellent thermal insulation and structural material with strong adhesion to the base material. It is widely used in exterior walls, pipes, refrigerator insulation and other fields. However, PUR has a loose and porous structure and is easy to burn. Its flame retardant performance has become one of the key technologies that will continue to be widely used in the future. The main method to improve the flame retardant properties of materials is to use flame retardants. Commonly used additive flame retardants include halogenated phosphates, non-halogenated phosphonates such as dimethyl (ethyl) methyl phosphonate, inorganic flame retardants such as ammonium polyphosphate (APP), encapsulated red phosphorus, expanded graphite, etc. . Additive flame retardants may lead to problems such as low compatibility, precipitation and reduced mechanical properties. Reactive flame retardants form covalent bonds with polyurethane and have attracted much attention due to their good compatibility, maintaining the inherent mechanical properties of polyurethane and obtaining better flame retardant effects at low concentrations.

Melamine is the most commonly used nitrogen-based flame retardant. Melamine resin is also called melamine resin. Its structure contains N element and has certain flame retardant properties. However, the flame retardant effect of a single N element is not ideal, so this project Introducing P element into melamine resin can enhance the flame retardant effect due to the flame retardant synergistic effect formed between N and P flame retardant elements.

Chinese patent CN110283207A discloses a phosphorus-nitrogen synergistic flame-retardant polyether polyol resin, whose representative structural formula is as follows: where R=R ₁ or 2≤n≤4, 2≤m≤4, x≥1. A method for preparing phosphorus-nitrogen synergistic flame retardant polyether polyol resin, the steps of which are: heating hexamethoxymethylmelamine (HMMM) and phosphate diol or aliphatic diol under the catalysis of p-toluenesulfonic acid An ether exchange reaction is carried out, and a phosphorus-nitrogen synergistic polyether polyol resin with polyhydroxyl groups is obtained through post-treatment. The process reaction conditions of this invention are complex and the cost is high.

Contents of the invention

The technical problem to be solved by the present invention is to provide a new method for preparing reactive melamine resin. The prepared reactive melamine resin has good flame retardant properties, long-lasting flame retardant properties, is non-toxic, and has little impact on the environment. advantage.

In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: a preparation method of reactive melamine resin, including the following steps in sequence:

(1) Add melamine, paraformaldehyde, methanol, and polyol into the reaction kettle in a molar ratio of 1:4 to 6:2 to 4:2 to 4 to form material I;

(2) Heating and raising the temperature under stirring conditions. When the temperature of the material in the reaction kettle is 50 to 75°C, add a pH regulator to adjust the pH of the system to 9 to 11. The reaction time is 2 to 3 hours to obtain material II;

(3) Add diethyl phosphite by dropwise addition under normal pressure. The dropping time is 10 to 60 minutes. The mass of diethyl phosphite is 1 to 3.5 times the number of moles of melamine to obtain material III;

(4) Material III is reacted at 50-75°C for 2-4 hours, and then a pH adjuster is added to adjust the pH to 7-8 to obtain material IV;

(5) Carry out vacuum distillation on material IV to separate small molecular substances in the system. The vacuum distillation temperature is 70~100℃, the pressure is -0.08~-0.10MPa, and the moisture test is less than 0.5% based on gauge pressure. Reactive melamine resin.

In the above technical solution, preferably, the polyol in step (1) is selected from at least one of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, and glycerin.

In the above technical solution, preferably, the pH adjusting reagent in step (2) is at least one of an aqueous solution of sodium hydroxide, potassium hydroxide or an alkaline organic amine; the pH is adjusted to 9-11.

In the above technical solution, preferably, the pH adjusting reagent in step (4) is at least one of an aqueous solution of sodium hydroxide, potassium hydroxide or an alkaline organic amine; the pH is adjusted to 7-8.

In the above technical solution, preferably, the small molecule by-product in step (5) is a mixture of free formaldehyde, water and methanol.

In the above technical solution, preferably, the vacuum distillation temperature in step (5) is 70 to 100°C.

In the above technical solution, preferably, the reactive melamine resin prepared in step (5) has the following general formula as its structural characteristics:

Where: R is -O(C ₂ H ₄ O) _m H, -O(CH ₂ CH(CH ₃ )O) _n H, -OCH ₂ CH(OH)CH ₂ OH or -

One of O(CH ₂ ) ₄ OH; where 1≤m≤2, 1≤n≤2;

R1＝Ror Among them, general formula (I) is the main product.

The invention provides a method for preparing reactive melamine resin. The flame retardant element phosphorus is introduced into the melamine molecular structure to achieve a synergistic flame retardant effect of phosphorus and nitrogen. At the same time, the structure contains more than two reactive groups -OH, specifically: Melamine, paraformaldehyde, methanol, and polyol are added into the reaction vessel at a certain molar ratio. Melamine and paraformaldehyde undergo a hydroxymethylation reaction under alkali catalysis to generate hydroxymethylmelamine, diethyl phosphite and hydroxymethyl Melamine reacts to generate melamine-based phosphate diol. At the same time, under the acidic conditions catalyzed by diethyl phosphite, hydroxymethyl melamine reacts with methanol to generate methyl etherified melamine formaldehyde resin. Methyl etherified melamine resin reacts with polyol to generate Melamine resin with a certain functionality was finally obtained as a reactive melamine resin, which achieved good technical results.

Detailed ways

The following are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All technical solutions falling under the ideas of the present invention should fall within the scope of protection of the present invention. For professionals and technicians in this technical field, there is no need to deviate from the scope of the present invention. Slight improvements and modifications made to the present invention based on the principles of the present invention should also fall within the protection scope of the present invention.

[Example 1]

(1) Add melamine, paraformaldehyde, methanol and diethylene glycol to the reaction vessel in a molar ratio of 1:4:2:2, and stir evenly to obtain material I;

(2) The material I is heated to 50°C, triethylamine is added, the pH is adjusted to 9, and the reaction is carried out under normal pressure with a reaction time of 2 hours to obtain the material II;

(3) Add diethyl phosphite dropwise to material II, the dropping time is 30 minutes, the molar ratio of the added diethyl phosphite to the melamine in step (1) is 2:1, and material III is obtained;

(4) Keep material III at 50°C, continue the reaction for 2 hours, add triethylamine, adjust pH = 7.5, and obtain material IV;

(5) Distill the material IV under reduced pressure to remove small molecule by-products. The vacuum distillation temperature is 75°C, the pressure is -0.098MPa, and the solid salt is filtered to remove the solid salt based on gauge pressure to obtain reactive melamine resin S _1. Its performance The data are shown in Table 2.

[Examples 2 to 6]

Embodiments 2 to 6 were carried out according to each step in Example 1, with the difference being reaction raw materials, raw material ratio, catalyst type and dosage, reaction time, reaction temperature, pH adjusting reagent and adjusted pH value, wherein the pH adjusting reagent Concentrations are all mass percentage concentrations, and the reaction conditions are detailed in Table 1.

Table 1 Raw material molar ratio and reaction conditions in the preparation of reactive melamine resins in Examples 1 to 6

【Comparative Example 1】

1. Synthesize phosphorus and nitrogen synergistic flame retardant polyether polyol with reference to the scheme in Example 1 of patent CN 110283207 A. The steps are as follows:

Add hexamethoxymethylmelamine (HMMM, 3.9g, 0.01mol) and phosphate diol (di-2-hydroxyethylamine methyl diethyl phosphate, FRC-6, 5.1g, 0.02mol) into 100mL In the three-necked flask, add p-toluenesulfonic acid (TsOH, about 0.005g) and N,N-dimethylformamide (DMF, 2g), and under nitrogen protection, magnetically stir at 120°C for 3 hours to complete the ether exchange reaction; Cool the reaction system to room temperature, add 2 mL of ethyl acetate and stir evenly, then add 12 mL of n-hexane under stirring conditions, let it stand for phase separation, and remove the supernatant; after repeating this 3 to 5 times, remove the viscous substance in the lower layer The solvent was removed by rotary evaporation at 55-70°C to obtain a brown viscous product: phosphorus-nitrogen synergistic flame retardant polyether glycol, with a yield of 95%.

Table 2 Index data of the reactive melamine resin prepared in Examples 1 to 6 and Comparative Example 1

It can be seen from the performance data in Table 2 that the conventional index performance data of the reactive melamine resin prepared in Examples 1 to 6 of the present invention is similar to that of Comparative Example 1, and the preparation process is simple, low cost, and the process adjustment scheme of the present invention is adopted. , the operation is simple, and the prepared reactive melamine resin can reduce costs and achieve good technical results without affecting conventional performance indicators, and can be used in the application of polyurethane foam.

Claims (5)

1. A preparation method of reactive melamine resin, including the following steps: (1) Add melamine, paraformaldehyde, methanol, and polyol into the reaction kettle in a molar ratio of 1:4 to 6:2 to 4:2 to 4 to form material I; (2) Heating and raising the temperature under stirring conditions. When the temperature of the material in the reaction kettle is 50 to 75°C, add a pH regulator to adjust the pH of the system to 9 to 11. The reaction time is 2 to 3 hours to obtain material II; (3) Add diethyl phosphite by dropwise addition under normal pressure. The dropping time is 10 to 60 minutes. The mass of diethyl phosphite is 1 to 3.5 times the number of moles of melamine to obtain material III; (4) Material III is reacted at 50-75°C for 2-4 hours, and then a pH adjuster is added to adjust the pH to 7-8 to obtain material IV; (5) Carry out vacuum distillation on material IV to separate small molecular substances in the system. The vacuum distillation temperature is 70~100℃, the pressure is -0.08~-0.10MPa, and the moisture test is less than 0.5% based on gauge pressure. Reactive melamine resin. 2. The preparation method of reactive melamine resin according to claim 1, characterized in that the polyol in step (1) is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and butylene glycol. At least one of alcohol or glycerol. 3. The preparation method of reactive melamine resin according to claim 1, characterized in that the pH adjusting reagent in the step (2) and step (4) is an aqueous solution of sodium hydroxide, potassium hydroxide or alkaline solution. At least one of the organic amines. 4. The preparation method of reactive melamine resin according to claim 1, characterized in that the small molecule by-product in step (5) is a mixture of free formaldehyde, water and methanol. 5. The preparation method of reactive melamine resin according to claim 1, characterized in that in the step (5), the vacuum distillation temperature is 75-95°C.